Questions about LiveIns and LiveOuts

I am very confused a question, what is LiveIns register or LiveOuts register means? Several registers inherit from current MBB’s precessors and not be killed, must they be transfered to successors? Some new registers defined in current MBB, are they also could be transfered? I am not sure if my understand is correct.

Additonally, is anyone has some docs about LiveIns and LiveOuts?

Any advice will be appreciated.Thanks in advance.