Cross References (or simply XREFs) is a feature of disassemblers to show you where certain functions and objects were called from or which functions and objects are used by a specific function. We can simplify it by relate to it as XREF-To and XREF-From. The referenced can be either Data or Code.
XREFs are a valuable resource when we want to figure out exactly where a function was called from or what functions the current function calls. This, as you understand, can be quite useful, so we don’t have to iterate the stack for frame pointers to look for the function that called the current function or alternatively searching by hand for a CALLs to specific addresses.
As can be seen in your screenshot, radare2 mentions that a specific address is referenced from ("XREF from") several different locations (addresses) in the code. Using radare's
ax? subcommands you can easily view XREFS. For example,
axt 0xfa1afe1 will show you Xrefs to
axf 0xfa1afe1 will show you Xrefs from