what is mac ? hey mac how ya doing ?

I watched an old film today where some yank was calling people mac or mack
what does it mean???
where do it come from?

whats that about ??

Hey mac(k) how ya doin?

 

I believe it was something or other to do with the scottish people who settled in the mountains and they always wore a coat called a mac and their name was macdougal or macbride etc so they just reffered to each oither as mac. the term went out of use in the early 1970's