In chat, the short code
[metaso] expands to
http://meta.stacexchange.com/ (no typo, the missing 'k' is the bug I'm reporting).
(And since this is too short a bug report, I'll note that I think that
[metaso] should probably point to meta.SO.)
Thanks for reporting the typo. That's fixed and will be soon deployed.
As for where
[metaso] should point:
You may have missed that meta.stackoverflow.com has been split into two sites that reflect its former split personality as a Meta for Stack Overflow and one for the whole network.
As such, Meta Stack Overflow is now a regular child-meta, no special treatment. That means that on Stack Overflow and Meta Stack Overflow,
[meta] should be used -
[metaso] was more often than not used to indicate the network meta, so it now points to it.
[metaso] is officially deprecated (it isn't documented anywhere any more), and we did convert
[metase] in old posts, but are keeping
[metaso] around for a bit longer, for the places we may have missed and for those who still use it, for now.