Destiny is what's meant to be, what's written in the stars, your inescapable fate. You might think it's your destiny to own a dog, but your sad goldfish survival rate should tell you that happy pets probably aren't in your future.
A noun meaning fate, destiny is synonymous with other nouns like divine decree, fortune, and serendipity. There's no avoiding destiny — it's going to happen no matter what you do. But before you get bogged down worrying about what the distant future holds, remember what Winston Churchill said: “It is a mistake to look too far ahead. Only one link in the chain of destiny can be handled at a time.”