Just call me Duncan. (And if you get the reference, hello fellow 80s kid!)
Zaiks is doing little guides for the character classes in his The Quest for Quests comic, and this one is Megan's. The man-at-arms is, as he describes it, a very generalized jack-of-all-trades warrior who can utilize a wide range of weapons, but who only has basic combat skills. Though they may have the option to specialize later.
Don't let any of that fool you, though. Megan can still kick names and take ass like a pro!
A more complete write-up may be found on his post here. While you're at it, why not check out his write-up on the Ranger class here, belonging to his pretty pom babe Maddy, too.
I've always described it as proficient with most if not all weapons. More than basic but certainly not expert. Basically can grab any weapon and have a really good chance of beating your ass in with it as they are the ones that keeps the armory.
In a story I had, the guy that was named 'Man at Arms' was a rather rough character that when an underling to the antagonist broke in. Grabbed the ballista (huge crossbow that launches arm sized bolts) and used it to send the underling packing 'airmail' by setting it on the nearest stone block that came loose and kicked the lever.
I've always described it as proficient with most if not all weapons. More than basic but certainly
