liberty的意思是“自由、许可”。take the liberty of 后接动词的ing形式，表示夺走了做某件事的自主权，而把这件事情做了。

to do something that will have an effect on someone else, without asking their permission

在未经他人允许的情况下做会影响他人的事情;擅自做…，自行作主干…

I took the liberty of booking theatre seats for us.

我自作主张给大家预订了戏票。