What does "LFF SATA" mean?

LFF == Large Form Factor == 3.5" hard drive

SFF == Small Form Factor == 2.5" hard drive

They had to start designating it since many servers and even desktops now are shipping with SFF drives to save physical space and/or cram more drives in.

To complement Peelman's answer, here is HP's official documentation on the topic of all the other disk vocabulary that goes with LFF and SFF:

Source/reference:

HPE Hard Disk Drives - a00001287enw - 15825 - Worldwide - V10 - 13-August-2018