I should tell you that most/all of these definitions are coming straight off the top of my head, but most of them should be right I hope. I'll definitely look stuff up if I'm not 90% sure! And feel free to yell at me if you think I've said something crazy. The Glossary is roughly in alphabetical order.

(I've thrown in some you'll probably never need to know, just for fun, hehe.)

* Aliasing

Often referred to as 'jaggies', aliasing is what occurs in renders when not enough samples are taken from the scene. The most common example is the stair-stepping effect seen along the edges of objects and highly contrasted areas of your image.

* Anti-aliasing

Techniques to combat aliasing like oversampling/supersampling and filtering.

* Adaptive Sampling

A technique used to anti-alias your image really well, while still keeping rendertimes low. Adaptive Sampling adjusts it's level of anti-aliasing over different parts of the image. Using less/more where less/more is needed etc. You need to tune these settings to work well for each scene.

* AO (Ambient Occlusion)

Ambient Occlusion is an effect that is often used in movie/TV animation as a replacement to GI or Final Gather. It is used as a replacement because it can be much faster to render and easier to control. It's called Ambient Occlusion because it does two things. It looks at the environment colour (which could be a flat colour, or could also be an image, eg HDRI) and applies some ambient lighting to the object based on that, then it also darkens the object in areas where there are creases, or anywhere else in which two or more surfaces are close together. The example render below shows two scenes in which only Ambient Occlusion was used, there are no lights. In Mental Ray, Ambient Occlusion is available to us via the Dirtmap shader (see the shaders section of this thread). A common technique is to render our your scene normally to get a Beauty pass, then render out a separate Ambient Occlusion pass for adding to your to final composite.

(click here to see an example render)

* BRDF (Bidirectional Reflectance Distribution Function)

More or less the way to describe how light interacts with a surface at any given point.

* BSSRDF (Bidirectional Sub Surface Reflectance Distribution Function)

Hehe, more or less the way to describe how light interacts with a semi-translucent surface at any given point. (ie skin, wax, other organic surfaces)

* BSP (Binary Space Partitioning)

BSP is a method of accelerating the raytracing calculations performed during rendering. BSP settings in Mental Ray can greatly affect rendering time!

* Caustics

The light patterns created by focussed refracted or reflected light.

(click here to see an example render)

Download the scene for Maya 5 or Maya 6

* Cornell Box

Not really a rendering term, but it's a type of scene sometimes used to illustrate examples of Global Illumination etc. A Cornell Box scene usually looks like a small room with different coloured walls, containing some cubes. Cornell university created a miniature scene like this (in real life) to observe how light bounces around in a scene. These days, people often test their fancy renderers by comparing a digital version of this scene to the real thing. For more info, click here to go to the website of the real Cornell Box.

* Diffraction

The effect of light being seperated into it's spectrum of colours when it is refracted through hard edged surfaces, like a prism.

(click here to see an example render)

It's not the nicest example but hey.

* DOF (Depth of Field)

The effect that creates out of focus blurring, for parts of your scene that are too close or far from the camera.

(click here to see an example render)

Download the scene for Maya 5 or Maya 6

* FG (Final Gather)

A Mental Ray feature that can be used for creating that classic 'GI' look, often used for showing off models. It can also be used for HDRI, object lights and for smoothing out GI.

(click here to see an example render)

Download the scene for Maya 5 or Maya 6

* GI (Global Illumination)

The simulation of realistic environmemt lighting. With a normal scene containing one spotlight in Maya, things that fall within the cone of the spotlight are lit, those that don't are black. Using GI, Mental Ray will calculate the way in which light bounces around a scene, creating secondary bounce light and other effects such as colour bleeding. Using Global Illumination can lead to extremely realistic lighting.

(click here to see an example render)

Download the scene for Maya 5 or Maya 6

* HDRI (High Dynamic Range Image)

An image file that contains much more colour and intensity information than a regular BMP or JPG file. Because these special images contain so much more data, you can actually use them to light your scene! The ultimate use of HDRI is to take photographs of a real-world set, then use HDRI to accurately light your Maya scene exactly the same way the real location was lit! All without lights! Common file extensions of HDR images are .HDR, .MAP and .TIF.

(click here to see an example render)

* IBL (Image Based Lighting)

A technique of lighting your scene with images rather than lights. HDRI being one such IBL technique.

(click here to see an example render)

* Micropolygon Displacement

The ability to create enormous detail through displacement at rendertime, on low polygon geometry. You don't need a really dense mesh to create detailed displacement, because Mental Ray can create any additional geometry at the micropolygon level (smaller than the initial polygon).

(click here to see an example render)

Download the scene for Maya 5 or Maya 6

* Ray

(I'm going to do my best to explain this, if you see something wrong then let me know!!)

A ray is basically an imaginary line that is 'cast' from one place in your scene to another in order to sample a property for rendering. There are quite a few different 'types' of rays depending on what needs to be sampled. Here are some of them and what they do:

Eye Rays: These are cast into your scene from the camera, through the pixels of your image, in order to sample which objects need to be rendered, and how the pixels they were cast through should look (more or less). These rays are used in both Scanline and Raytracing renderers.

Reflection/Refraction/Secondary Rays: These are cast from each point on a surface (that an Eye Ray has hit) that is reflective/refractive, out into your scene to determine what should appear in that reflection/refraction. These rays are only used by Raytracing renderers, or when the Raytracing feature of a primarily Scanline renderer (such as the Maya Software renderer) is turned on.

Light Rays: These are cast from each point on a surface (that an Eye Ray has hit) towards the lights in your scene, to find out the properties of the light.

Shadow Rays: When using Raytraced Shadows, an Eye Ray has been cast from the camera to your object, then a Light Ray goes from that point on the object to a light source, then finally a Shadow Ray is cast from the light, back along the same path as the Light Ray to see whether anything is blocking the light from your object. If something is blocking the Shadow Ray's path, then obviously that point on your object must be in shadow. This ray type is only used by Raytracing renderers or the Raytracing feature of a primarily Scanline renderer.

* Raytracing

Raytracing is a rendering process that can calculate things like reflections, refractions, GI and other complex rendering effects. Raytracing is often thought to be slow, though these days a lot of renderers such as Mental Ray and Brazil are built for speed when raytracing.

* Scanline Rendering

A fast rendering process that renders your scene one row of pixels (one scanline) at a time. Scanline rendering is often fast, because it doesn't calculate things like reflections, refractions, and other more complicated rendering effects.

* SSS (Sub-Surface Scattering)

The effect of light penetrating a surface and illuminating the inner layers. This is very important when creating realistic skin and most other organic materials. For example, if you (in real life, hehe) press a strong torch up against your hand, you should be able to see the light illuminating your hand from the other side.

* Texel

A pixel that is part of a texture map.

* Uniform Sampling

A method of anti-aliasing that applies the same amount of anti-aliasing to the whole image. It can give great results but can be pretty slow.

* Voxel

A volume of pixels. For example Maya Fluid Effects uses voxels, it isn't real geometry (unless you tell it to be), just a volume of pixels!

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