1. in addition to your main job
兼职

例句：

He makes a little money on the side by cleaning windows in his spare time. 他靠业余时间兼职清洗窗户赚些零用钱。

2. secretly
秘密地

I think he has another woman on the side (= a relationship with a woman who is not his wife). 我认为他还有别的女人。

3. (mainly US, of food in a restaurant) served on another plate, or on the side of the plate
（主要在美国，餐馆中的食物）装在另一个盘子里；作为配菜

例句：

May I order a salad on the side? 我可以点一份配菜沙拉吗？

I’d like a salad with the dressing on the side (= with the dressing served separately from the salad), please. 我要一盘沙拉，调味汁单独盛盘，谢谢。

I’ll have a omelette with fries on the side, please. 我要一个煎蛋，另要一盘炸薯条，谢谢。