"HOLD ON" 可以依照不同情况就有好几个不同的用法和解释.
通常的意思有：坚持住!继续；等一等（停住）；忍住；抓住,等等不同解释.
给你几个例句应该比较容易明白：
◆讲电话时：“Please hold on.请稍候”或 “Hold on,please.请不要挂断.”
◆叫住别人时：Hold on,please.请等一下.
◆Hold on!buddy －－兄弟,要挺住啊!
◆Hold on a minute while I get my breath back.停一停,让我喘口气.
◆ He held on to the rock to stop himself slipping.他紧紧抓住岩石以免往下滑.
◆You should hold on to your shares.你应该继续保留（持有）股份.
◆I don't think I can hold on much longer.我觉得自己坚持不了多长时间了.