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
Used primarily after something has been accomplished.
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".