Occasional means happening sometimes but not regularly or often. An occasional thunderstorm might roll through your town a few times each summer, but not every week. Your teacher might give occasional pop quizzes, keeping everyone alert without making tests a daily event.

The word suggests something happens now and then, with gaps in between. If you're an occasional visitor to your grandmother's house, you go there sometimes but not on a set schedule. If you make occasional mistakes in spelling, you get most words right but slip up here and there.

Occasional sits between “rare” and “frequent.” A rare event almost never happens. A frequent event happens all the time. An occasional event falls comfortably in the middle: it happens often enough that you recognize it, but not so often that you can count on it or predict exactly when it will occur next.

You might be an occasional reader of mystery novels (you enjoy them when you pick one up, but you read other genres too), or you might enjoy an occasional ice cream cone (a treat you have sometimes, not every day).