Burglary - in California

California Penal code 459 states that a burglary is:

459.  Every person who enters any house, room, apartment, tenement,
shop, warehouse, store, mill, barn, stable, outhouse or other
building, tent, vessel, as defined in Section 21 of the Harbors and
Navigation Code, floating home, as defined in subdivision (d) of
Section 18075.55 of the Health and Safety Code, railroad car, locked
or sealed cargo container, whether or not mounted on a vehicle,
trailer coach, as defined in Section 635 of the Vehicle Code, any
house car, as defined in Section 362 of the Vehicle Code, inhabited
camper, as defined in Section 243 of the Vehicle Code, vehicle as
defined by the Vehicle Code, when the doors are locked, aircraft as
defined by Section 21012 of the Public Utilities Code, or mine or any
underground portion thereof, with intent to commit grand or petit
larceny or any felony is guilty of burglary. As used in this chapter,
"inhabited" means currently being used for dwelling purposes,
whether occupied or not. A house, trailer, vessel designed for
habitation, or portion of a building is currently being used for
dwelling purposes if, at the time of the burglary, it was not
occupied solely because a natural or other disaster caused the
occupants to leave the premises.

There is a lot of language here, but in essence a burglary is the unlawful,
entering of a dwelling (or place of business) with the intent to commit a
crime. Under the old common law the requirements were very strict
and could be hard to prove. Today, the prosecution needs to prove that
you the defendant, entered a building (or other specified areas) with the
intent to commit a crime. The hard part hear for the prosecution is
the intent aspect. If you were in a store and picked something up and
put it in your cart but forgot to put it on the stand you will probably not
get charged with burglary. Things change if you put it in your purse and
walked out of the store.

Each case of burglary is heavily dependent on the facts and you should
consult an experienced attorney to help you with any matter you may have.