Grand Slams in Baseball, Golf and Tennis are well defined. Not so much for birding. This Blogpost details 2 recent Birding Slams for me: 5 Falcon species in a day and the 4 Zonotrichia Sparrow species at a single place - and a "sorta slam" - Four Finch species on the four perches on a feeder at the same time.
http://blairbirding.com/2022/02/04/slamming/