"AXIA" denotes a certain "stepping" (microcode revision) of the Thunderbird CPU. What the letters mean exactly is probably known only to the inside guys at AMD.
Generally the CPU's stepping only makes a difference if you plan to overclock. "AXIA" is one of the later steppings and is a good overclocker's stepping; there's also an even more recent stepping, "AHJYA" I believe, that overclocks even better than AXIA.
A little bit of trivia: I believe when AMD (or Intel) releases a new stepping for a CPU, they discontinue the old stepping (since deploying a new stepping only adds a one-time overhead cost associated with adjusting the assembly line). This means that any "AXIA" CPUs out there are just old stock that isn't flushed yet.
Kelledin
"/join #hackerz. See the Web. DoS interesting people."