Penal Code Section 316: Keeping Disorderly or Assignation House:
Every person who keeps any disorderly house, or any house for the purpose of assignation or prostitution, or any house of public resort, by which the peace, comfort, or decency of the immediate neighborhood is habitually disturbed, or who keeps any inn in a disorderly manner; and every person who lets any apartment or tenement, knowing that it is to be used for the purpose of assignation or prostitution, is guilty of a misdemeanor.
Layman terms it can be keeping a whorehouse, or a place where prostitution takes place. This charge is most commonly associated with massage parlors, strip bars, topless clubs, or other adult services. It is common for a prostitution bust on local businesses to also include charges for PC 315 or PC 316 for the owners.
While this is a misdemeanor crime, it is also very serious and can lead to jail time, show up on back ground checks, and cause license suspensions, revocations, or even cause an issuing agency to decline to issue a license to an applicant. A conviction may also show up on background checks for job applicants, which could lead to an impediment to future employment.