Virtual Extensible local area networks (VXLAN) is a data plane technology that extends virtual LAN (VLAN) functionality into Layer 3. These Layer 3 technologies replace the use of the Layer 2 Spanning Tree Protocol (STP) loop prevention protocol in order to enable the use of all available paths. VXLAN uses MAC-in-UDP encapsulatioon method to extend Layer 2 and Layer 3 overlay networks over existing Layer 3 infrastructure.

A virtual network identifier (VNI), sometimes called VNID, is a 24-bit identifier that defines the broadcast domain. the VNI is similar to a Layer 2 VLAN ID field. However, a VLAN ID is only 12 bits in length. Becase a VNI is 24 bits in length, it is theoretically possible to create up to 16 million VXLAN overlay networks within a single infrastructure.

A virtual tunnel endpoint (VTEP) is a device that encapsulates and decapsulates traffic in a VXLAN fabric. A Network Virtual Endpoint (NVE) is a logical interface that encapsulates and de-encapsulates the traffic.

Reference: VXLAN terminology