When you do something useful for the world. It can be anything big or small, long-term or a once off. Something that you wish more people just did, anything that you've wanted to do for ages but haven't got round to, or just something nice for someone.
"I just spent an hour helping out my friends housemate by drying and putting way all their dishes." "For no reason? you just did a Useful Act"
I'm going to tell people how important and wonderful they are, to their faces while they're there. Rather than think it after they leave.
"Just got my bike fixed so that I can replace one unnecessary drive per week with a bike ride instead" "I've been meaning to do that! It's such a Useful act"
"I got to netball early tonight, so instead of just sitting by myself for 30 minutes like usual, I scored a game with no subs so that the players on court wouldn't have to. It kept me occupied and was a Useful Act"
"I want to spend more time playing with my dog, it's a useful act"