Meaning Awesome or incredibly. But primarily used in reference to Usain Bolt, the world’s fastest man. The term was coined as part of a promotion by CarMax called “Usainly Fast Offers” where CarMax challenged Usain Bolt to race against their super fast online offers.
Dang, that was a usainly good commercial!
I just got a usainly fast offer on my car from CarMax
Your dad is packing an entire shed's worth beach accessories into the boot of the car for a big trip to Portstewart during the summer holidays. He loads the last item into the back, turns to your mother and says, "ATS US NAI".