Term used by a group of people smoking weed to initiate a phase in which only allows one hit per time around the circle.
"p" stands for puff or pull off a joint.
"1" refers to the number of those puffs or pulls.
It usually begins when a joint becomes of roach, or has less than 25% of it's smokable content remaining.
Previously smokers would be taking two or three hits from the joint, however once 1p is initated only one hit is allowed.
It is done to save weed and to ensure that everyone gets an equal amount.