I've been using it as very specifically manipulating buttons, blocks, and aggro... as well as anything else that isn't inflicting damage/status effects. Argent peacemaker is the greatest for these things.. dark retribution has a few tricks up its sleaves, and gran faust is a relatively poor at this.
But other people seem to be describing things like poisoning enemies as utility?
Basically anything that makes a situation much easier to deal with that doesn't necessarily have to deal with damage. A unique trait to a weapon, you could say.
Antigua has block breaking and simplified controllable aggro utility.
Sealed Sword has great knockback utility.
Mist Bombs have crowd control utility.
...and so on.
Hm. I'd always thought of it a bit differently, but very much similarly.
Being able to stop enemies from healing (poison), locking enemies in place (freeze), or manipulating their attack patterns (stun) are all examples of statuses giving 'utility'.
I see it as 'anything that makes a situation more manageable that isn't purely damage or defense'. For instance, ASI makes dodging easier and influences the timing of your combos, or a Divine Avenger knocking enemies away with a charge attack.