Criminal conversion is the crime of exerting unauthorized use or control of someone else's property. It differs from theft in that it does not include the element of intending to deprive the owner of the possession of that property. As such, it is a lesser included offense of the crime of theft. Criminal conversion specifies a type of conversion in that it involves criminal law, not civil law.
An example might be tapping someone's secured wireless LAN or public utility line (which could also amount to theft of services). Another example might be taking a joy ride in a car, never intending to keep it from the owner. Some places have defined such conduct as a specific type of theft, perhaps with a modified penalty.
Note that the "unauthorized" use may begin after a period of authorized use, where, for example, a person rents a car then keeps it for an extra week without permission from the rental company. Another common example occurs when a person fails to report finding lost goods (including animals), intending only to keep them until someone asks for their return. When the intent becomes one of keeping the property, it is a theft.
Other articles related to "criminal conversion, conversion":
... In England and Wales, the term fraudulent conversion was applicable to the offences under the Larceny Act 1901 and under sections 20 and 21 of the Larceny Act 1916 ... The former offences of fraudulent conversion are replaced by the new offence of theft, contrary to section 1(1) of the Theft Act 1968 ...