From BlenderWiki

Static object type

Physical object, but not affected by gravity.

Actor

This causes the physics engine to evaluate your object, causing your object to be seen as more than part of the world (a simple wall or floor). This object can now be seen by other active objects.

At this point your object is not affected by normal physics (e.g. gravity) but is seen as more than just a background object. This is useful for interaction between objects that need not have physics properties, such as gravity, e.g. a button on a wall.

Ghost

Ghost gives the object the ability to pass through other objects. This helps save processing time while calculating objects’ physics (e.g. bouncing, friction, etc.). A collision with another object is still detected and reported to your game logic.

Invisible

If the object is set to "Invisible", it isn't rendered in the Game Engine.

Advanced

Collision advanced settings.

Anisotropic

This controls the direction of friction in the X, Y or Z direction of the object. Anisotropic is relative to the amount of friction in a particular direction. For example, take the wheel of a skate board, the forward direction should rotate easily, yet a sideward motion should be difficult and decreased by a higher level of friction.

Bounds

The Blender Game Engine has a number of ways of dealing with the shapes of objects. The reason that the game engine avoids highly accurate, per face object collisions, is due to the high level of processing power that it would demand. It is often faster, during game play, to uses a simpler system such as a box or a sphere for an object that’s shape is very similar.

The bounds are calculated from the object’s centre, which is designated by the pink dot normally at the centre of your object. It is not uncommon or useful to move this centre to a more convenient location. This can be done in the Editing context (F9) and choosing one of the 3 options that focus around Centre movement (see Mesh for more info).

Convex Hull and static Triangle Mesh are designed for uses with World objects floors, walls, trees, etc.

Blender has no generic way of interacting with hollow objects. An example, which would be difficult to create, would be a cup to shake dice in.