When exiting Vim or trying to close the terminal window in another way, {how} defines whether the job in the terminal can be stopped. When {how} is empty (the default), the job will not be stopped, trying to exit will result in E947. Otherwise, {how} specifies what signal to send to the job. See job_stop() for the values.

After sending the signal Vim will wait for up to a second to check that the job actually stopped.

Can also be used as a method:

GetBufnr()->term_setkill(how)