Rabbit is a free-for-all game type where the goal is to grab the flag on the map and survive with it as long as possible. A Rabbit map will have one flag that starts at a central location. All players who are not carrying the flag cannot damage each other. However, once someone grabs the flag, he can damage everyone, and everyone can damage him. A player will get a point for every second that he has held the flag, as well as a point for every player he kills.
LakRabbit is a much more popular variation of the original Rabbit with several changes. The goal in LakRabbit is not to survive with the flag, but rather to shoot people in mid-air. As before, everyone must attack the flag carrier and vice-versa, but players will get a lot more points for hitting mid-airs then they will for getting regular kills and holding the flag. LakRabbit also has several more less significant changes, such as spawning with your selected loadout, a 'bouncy' out-of-bounds grid, and more. LakRabbit was modded by borLak.
There are many Rabbit mods similar to LakRabbit, and most of them predate it - such as MinRabbit and Caerbannog, but LakRabbit is the one that has persisted the most over the years.