Meaning outstanding, wonderful, better than everything else, stellar is a word of praise or excitement. Thomas Edison invented many things, but his stellar achievement might have been the light bulb.
Stellar literally means "like a star." When it comes time for your debut on Broadway, you will sure hope that the reviews say that you delivered a stellar performance. You could also use stellar to talk about actual stars, of course, or you could even blend the two: enjoy the stellar beauty of your beloved under the stellar light of a moonless night.