It's the present participle of the verb "Reminisce", which is a synonym for the verb "Remember".
It is a very classy verb used by various poets and people of higher status.
It was also made famous by rapper Tupac Shakur's "Pour out a little liquor" song which made various Afro-American L.A. gangsters use it while smoking weed and drinking liquor with their bitches in the club.
Person 1 : Yo wazzup man! Watchu u doin here sHHmokin' that weed all alone?
The act of using alcohol, especially rum and tequila, to try and remembersomething from the past. It is used on both happy and sad occasions by people with both elephant-like and poor memory.