[Brian_K_White]

xterm, the term used in error to refer to the definition of a particular terminal, is used by several different implimentations going back decades and spanning many platforms.

Those implimentations not only all assert the exact same "TERM=xterm" by default, many of them even name the executable the same "xterm", yet do not all adhere to any single common standard. The SCO OSR5 xterm is different from old versions of Xfree86 xterm is differrent from the current xorg xterm etc. There is some overlap, but not nearly enough. The differences are not merely small superset/subset feature differences like 256 color support etc. They include, as I did say, totally differrent F-keys and arrows for example.

That is what "xterm is not a standard" means.

It's a word that refers to a range of different definitions that depend on context, not a single specific definition that always means the same thing in any context, and so is not a meaningful definition, or standard.