a jump is anything that can get you to a place noone else can get to without knowing of that jump. it's finding little ledges and angles in the game that can support or bounce a player from one location to another. Usually up. If you ever join a CoD server and join a Neuville map, most likely you'll see someone on the roofs when no ladder or staircase is present (neuville has been jumped to often, it's getting to be the noobs can do most of them).
nade jumping is using the explosion of a grenade to give you a couple more inches of boost. allowing you to reach places normal jumping can't
panzer jumping is using the knockback of the panzerfaust when you shoot to boot yourself. generally used when there is no place for a grenade to land, sit and explode
strafe jumping is a technique to allow you to jump a couple extra feet (generally 5-8 in-game) to reach places normal "w+spacebar" can't
Once you own at the game, it gets boring with all the newbs, so you join "jump servers" where you hone your skills at jumping, balancing, and finding "exploits" to the game's mapping. real fun actually. a totally new way to look at a game