Java Transaction API is a Java EE API that allow distributed transactions to be committed across multiple databases. JTA is a specification developed under the Java Community Process as JSR 907.
When PRPC is installed as an Enterprise tier application (and the XA version of database drivers are installed) the Commit and Rollback methods apply to both internal and external classes, implementing a distributed transaction. Informally, this is known as "two-phase commit".
For more information, see Distributed Transactions and PegaRULES Process Commander, a document on the PDN.