A "contender" is someone that might be able to win something. This is a little different from a "contestant". A "contestant" is anyone who enters a competition. But the real "contenders" are only the people who have a good chance of winning.

The phrase "Oscar contender" is commonly used to talk about movies and actors who might be nominated, or might win, an Academy Award. Here are some other common types of "contenders":

a presidential contender

a playoff contender (for a sports championship)

an Olympic contender

And here are some adjectives that describe contenders:

the leading contender

a serious contender

a strong contender