Ooops, nearly forgot you.
An old-style texture pack is one that installs into Texures and not a subfolder. All of the ones you can download are like that at the moment.
When you get close to a textured object, you can see the individual texture pixels, unless the object is rendered using inerpolation. Games choose to use interpolation for some textures and not for others. Forced smoothing ignores the game and always interpolates.
Mipmapping stops textured objects that are far away looking fizzy, but loses a bit of sharpness. I always enable it.
Judder fix is difficult to describe, but is to do with getting games to run at their correct speed.
Caching of small textures avoids the creation of new host textures for small textures that are repeatedly created from Glide (such as the green text in Descent II).
Disabling LFB reads, saves Glidos the trouble of actually finding out what is currently on screen when the game tries to read it.
Delayed writes puts off direct writes to the LFB until a buffer swap.