Collision usually refers to the scripting calls related to collision events. A collision will occur when an object or avatar collides with something.
Bump (or push) is another word for collide.
Example LSL Script[]
default {
collision_start(integer num_detected)
{
llSay(0,"I Collided!");
}
land_collision(vector pos)
{
llSay(0,"I Collided With Land!");
}
}