When the word "pimp" is used to define a person who runs a prostitution ring, it stands for "prostitutes in my possession." The acronym "pimp" has other meanings, too.
Additional definitions for the acronym "pimp" include: "people inflicting much pain," "player in massive proportions" and "paper in my pocket." Since there are several definitions for this acronym, the actual meaning of the word depends on the context in which it is used. Many people think of the word "pimp" as it relates to prostitution or gangster culture, so "prostitutes in my possession" is likely the most relevant definition for the word.