Pro equipment for a guitarist usually means a decent guitar (preferably with a backup guitar just in case), long guitar cables or a wireless unit, an amp powerful enough for clubs, an effects rack or pedal box that won't crap out, a decent microphone with a stand for backup vocals and stage clothing so you don't look like you walked in off the street.
In other words, ready to go on the road without looking like an amateur.

It's also a hint that they want somebody with stage experience who won't freeze up in front of an audience.

ie, one band I joined they gave me one week to get a haircut, find stage clothes and learn 40 songs. By the Monday of the next week I had to take over from the old guitarist without screwing up.