In the Confused State of CA
A caterer is regulated and permitted by the local health Department. A caterer is a person, business, or food facility that prepares, transports, and serves food at public and/or private events. The food is stored and prepared in an approved, permitted, permanent food facility, regulated under the California Retail Food Code (CRFC) through an annual health permit. There are two types of caterers:
Type 1: A fixed restaurant facility that also caters. This facility holds a health permit that allows catering (i.e., the permit should designate the facility as a caterer). Prior to any catering, the restaurant is required to submit a separate plan review of the catering operation for review and approval by this Department.
Type 2: A caterer who utilizes a permitted kitchen, provides a written agreement for use of that kitchen, and obtains a catering permit. The caterer is required to submit a complete plan review of the catering operation for review and approval by this Division prior to obtaining a health permit and beginning operation.The caterer is required, among other things, to submit a "Verification of Commissary" form.
A caterer is required to prepare all food at an approved food establishment, with the exception of barbeque. If a caterer is preparing and serving food all day at a public event (e.g., a booth at the County Fair), the operation is then a Temporary Food Facility, requiring a different health permit and permit fee.
http://www.edcgov.us/emd/envhealth/pdf/CalCode.pdf