Something excellent is very good, great, or high quality: this is one of the best compliments around.
Words like extraordinary and exceptional are similar in meaning to excellent. This is a strong word used mainly for things, people, and actions that are much better than average. A B+ on a test isn't bad, but an A is excellent. In basketball, making an all-star team is excellent. Being excellent is difficult and people tend to admire it. People use excellent in another, less specific way sometimes. If you want to say "Cool" or "Good" you might say "Excellent!"