Reserved people do not often talk about or show their feelings or thoughts.

a quiet, reserved woman 一位安静、矜持的女子

The English have a reputation for being reserved. 英国人以矜持闻名。

Reserved tickets, seats, etc. are ones that you have arranged to be kept for you

May I sit here, or is this seat/table reserved? 我可以坐这儿吗？还是这个座位／餐桌已经被预订了？