副业在英语中有多种表达方式，以下是一些常见的用法：

side job或 secondary job。

例句：I have a side job as a freelance writer in addition to my full-time job.

side hustle。

例句：She runs a side hustle selling handmade crafts online.

avocation或 by-line或 bywork或 parergon。

例句：His avocation is photography, and he often does freelance work for local businesses.

sideline。

例句：He has a sideline in real estate investing.

by-business。

例句：She started a by-business of selling homemade jams.

这些表达方式都可以用来描述一个人除了主要职业之外所从事的其他工作或经营活动。根据具体的语境和需要，可以选择最合适的表达。