In Chicano Slang it is mostly a derogatory term meaning older woman. Also means a tried woman, as in having been through the trials of life and living.
Can also mean an older woman of the barrio or older chola.
Meant to describe a girlfriend that has stayed by her boyfriend's side through difficult times, with an affectionate undertone. Also, to describe in light, derogatory (sometimes affectionate) terms a tried or worn woman no matter the age, identifying her presumed life experience.
When the older cholos referred to their girlfriends, they meant that they've been hanging around for a while. Better translated as 'old lady' as in "I'm a hang with my old-lady today."
El morro se agarro una bien ruca! (The youngster got himself an older/worn woman!)
She's been smoking since she was a kid, she's only 19 pero ya esta bien ruca. (but she's already old)