What is an epad in SIM MFF2 layout
It stands for exposed pad. They're intended for PCB heatsinking; you solder it to a large copper plane to pull heat away. They're often, but not always, internally connected to ground--look at the datasheet to see what it's connected to for this particular chip.
As an aside, if you're using a chip with an exposed pad, you should definitely use solder paste. Hand-soldering is pretty much not an option.