Words that are short for something else.
Ad is short for advertisement.
An ATM is an Automatic Teller Machine. You put your keycard or credit card into it to deposit or withdraw money.
Bike is short for bicycle. More people use the short form bike than the long form bicycle.
Bayerische Motoren Werke AG, shortened to BMW, is a German car maker that also make motorbikes and engines.
Budgie is a short form of budgerigar.
A bug is a slang word for any insect or anything that is like an insect, for example a spider.
You might also use bug as another word for annoy, as in "stop bugging me".
A bug is also a covert listening device, used to spy on what other people are talking about.
Chimp is short for chimpanzee.
A cop is a slang word that is short for a police officer.
Flu is the shortened or slang form of influenza.
A fridge is a short form of the word refrigerator.