Abbrievation for "grandpa", or "grandfather".
Grandfather (noun):
A patronly figure that you spend a lot of
time with, your "grandfather" figure.
Someone "
cool" in an "old-person" sort of way.
Grandfather (adjective):
Something/one that is "old school".
1. "Dude, this has been so
great to get icecream. You are like a/my grandpa!"
2. "This vintage
clock is sooo g-pa, man, take a look!"