The following definitions are applicable to this article:

1. "Premises" includes the term "building," as defined herein, and any real property.

2. "Building," in addition to its ordinary meaning, includes any structure, vehicle or watercraft used for overnight lodging of persons, or used by persons for carrying on business therein, or used as an elementary or secondary school, or an inclosed motor truck, or an inclosed motor truck trailer. Where a building consists of two or more units separately secured or occupied, each unit shall be deemed both a separate building in itself and a part of the main building.

3. "Dwelling" means a building which is usually occupied by a person lodging therein at night.

4. "Night" means the period between thirty minutes after sunset and thirty minutes before sunrise.

5. "Enter or remain unlawfully." A person "enters or remains unlawfully" in or upon premises when he is not licensed or privileged to do so. A person who, regardless of his intent, enters or remains in or upon premises which are at the time open to the public does so with license and privilege unless he defies a lawful order not to enter or remain, personally communicated to him by the owner of such premises or other authorized person. A license or privilege to enter or remain in a building which is only partly open to the public is not a license or privilege to enter or remain in that part of the building which is not open to the public. A person who enters or remains upon unimproved and apparently unused land, which is neither fenced nor otherwise enclosed in a manner designed to exclude intruders, does so with license and privilege unless notice against trespass is personally communicated to him by the owner of such land or other authorized person, or unless such notice is given by posting in a conspicuous manner. A person who enters or remains in or about a school building without written permission from someone authorized to issue such permission or without a legitimate reason which includes a relationship involving custody of or responsibility for a pupil or student enrolled in the school or without legitimate business or a purpose relating to the operation of the school does so without license and privilege.