letter是什么意思

例句：

1、Why write a letter to your future self?

为什么要给未来的`自己写一封信呢？

2、Perhaps they are afraid the imaginary letter will come true.

也许他们害怕那封虚构的信会成为现实。

3、 An important letter served the lawyer as evidence.

一封重要的信件被律师作为证据。