in the side和on the side的区别?

on the side的意思是：
1.〈非正〉作为兼职〔副业〕
He is a mechanic who buys and sells cars on the side.
他是一个兼营买卖汽车的技工.
2.暗地里,秘密地
She's married but she has a lover on the side.
她虽然已婚,但暗地里还有一个情人.
in the side 的用法没见过,你最好拿来例句说的更清楚些.