The law recognizes that owners of property have inherent rights, perhaps the most important being the right to the "exclusive" use of their property. A defendant will be liable for trespass if he or she enters the plaintiff's property without the plaintiff's consent and interferes with the landowner's exclusive right to use the land.
As generally used, "trespass" occurs when either: (1) a person intentionally enters another's land, without permission; (2) a person remains on another's land without the continued permission to be there, even if he entered rightfully; or (3) a person puts an object on (or refuses to remove an object from) another's land without permission. Note that the term "trespass" refers only to intentional interference with another's interest in property. If one accidentally enters another's land, this is generally not trespass.
For example, a burglar who intentionally enters someone's home commits trespass. On the other hand, if you have an unexpected epileptic seizure while driving your car and end up driving across someone else's lawn - causing damage to the property - you are not liable for trespass.