A decision problem is a question that requires a definite answer of "yes" or "no."
A problem is decidable if we can always construct an algorithm that correctly answers the problem.
P is the class of problems that can be solved in polynomial time. NP is the class of problems whose solutions can be verified in polynomial time.
The P versus NP question asks whether every problem we can quickly check can also be solved quickly. It focuses on whether problems where solutions can be verified efficiently can also have their solutions found efficiently.
If you resolve the P versus NP question, you will be $1 million richer. P versus NP is one of the Clay Mathematics Institute Millennium Prize Problems, which offers a million-dollar prize for solving it.
GeeksforGeeks - Decidable and Undecidable Problems
GeeksforGeeks - P vs NP Problems