Be there or be square什麼意思

"Be there or be square" is an English idiom that means you should be present at an event or activity, or else you will miss out on something important or interesting. The phrase suggests that not being there is equivalent to being out of shape or outdated, implying that you will be left behind if you do not attend. It is often used as a way to encourage people to join in or come along to an event.