What does XnAP stand for?

Xn Application Protocol

XnAP is a control protocol that is utilized between gNBs to enable a number of RAN procedures, including establishing Dual Connectivity, coordinating Xn-based handovers, data forwarding, and RAN Paging. During the handover, the source gNB will provide the target gNB with all of the information it requires to handle the subscriber, including security and User Plane connectivity. The Master gNB will use XnAP to set up a Secondary gNB for Dual Connectivity, with each gNB servicing the user at the same time.