Pop star- Singer of Popular music(pop music, the stuff you hear on the radio)
Pop culture- Popular culture(food, art, music can all be regarded as examples of PC along with many others)
Pop- Fizzy(carbonated) drinks such as Pepsi are called pop in the USA
When you open a bottle of champagne the air makes a popping sound as it is released through the neck of the bottle.
When you are on and aeroplane , your ears 'pop' as the altitude changes.
We also use 'pop' in 'are you going to pop the question?
Which means: Are you going to propose to her?