I have rewatched all the ghost in the shell movies/series and realized that the concept of "ghost" has kinda eluded me. I understand that "ghost" is the thing that makes someone actually "alive", but what is it really? What is a ghost?

i have been looking for the name of a soundtrack in the seven deadly sins and i haven't found it, so can you help me to find it. In season 2 episode 5 it started at 10:29 (time of the episode) when Merlin was fighting with Galand.