As someone who was recently new to League of Legends, I understand that some of the terminology can be confusing. There are a lot of acronyms used during gameplay that you might not be familiar with, so I thought I would share my knowledge with new players here
KS = Kite Safety
This person is complimenting you for your impeccable kite safety. Safety is always an important part of flying kites, so make sure to thank the person for noticing.
ULT = Ulterior Motive
A warning that one of your teammates may be scheming against you. Be careful.
FEED/FEEDER/FEEDING = I'm going to get some food
This person is hungry and is taking a break from the game to eat.
FARM = Literal farming
This person is informing their team that they dream of becoming a farmer. It's not really relevant to the game.
CARE = I don't care
This person is responding to the last thing said in a sarcastic way, indicating that they don't care.
JUNGLE = Stay out
A warning that the jungle in the game is dangerous and full of insects. Stay out at all costs.
BD = Big Damage
This person wants you to get more damage items.