1. 次要活动;附带事件;附属活动
A sideshow is a less important or less significant event or situation related to a larger, more important one that is happening at the same time.

2. (马戏或游园会中穿插的)小节目，助兴表演,杂耍
At a circus or fair, a sideshow is a performance that you watch or a game of skill that you play, that is provided in addition to the main entertainment.

1. a minor show that is part of a larger one (as at the circus)

2. a subordinate incident of little importance relative to the main event

e.g. instruction is not an educational sideshow