What is the meaning of boot?

Money or other property that is not like-kind, which is given to make up any difference in value or equity between exchanged properties.' boot' may be in the form of cash, notes, gems, the market value of an asset such as a mortgage, land contract, personal property, goodwill, a service or a patent offered in an exchange. The taxable gain in the like-kind exchange is recognized immediately to the extent of boot, whereas, other gain from the exchange may be deferred until subsequent transfer. (See exchange, like-kind).