Advanced eXtensible Interface

The Advanced eXtensible Interface (AXI) is an on-chip communication bus protocol and is part of the Advanced Microcontroller Bus Architecture specification (AMBA). AXI is royalty-free and its specification is freely available from ARM. AMBA AXI specifies many optional signals, which can be included depending on the specific requirements of the design, making AXI a versatile bus for numerous applications.

Source: Wikipedia — Advanced eXtensible Interface (CC BY-SA 4.0)