A related party exchange is a 1031 exchange where either the buyer of the relinquished property or the seller of the replacement property (or both) is considered “related” to the investor doing the exchange. There are special rules and restrictions on the ability to defer tax in a 1031 exchange that involves related parties.
See article below for more informaton on related party exchanges
An Overview of Related Party Exchanges
Receipt of Non-Like-Kind Property is Not Fatal to a Related Party Exchange