[ubuntu] terminal question

when I open a terminal my prompt says: "greg@greg-System-Product-Name:~$". There was a time when greg was good enough, then something else and, now, this. At the same time, when I am in files, there is no problem in that my home directory is /home/greg/ I don't understand why everything isn't as presented with files or where that other stuff is coming from.

Thank you.................