PDGF - Power and Data Grapple Fixture
FRGF - Flight Releasable Grapple Fixture
These can be grabbed by the ISS robotic arm to allow the spacecraft to be positioned for berthing.
You can get the forum software to enable pop-up definitions of all acronyms that are in the existing acronym list (but not all acronyms are in it!).
In the menu bar select the following sequence:
Profile - Look and Layout (Modify Profile section) - check the "highlight items from Acronyms List" box
After that all acronyms in the list will be underlined with a dotted line - then just hover over with mouse to see the definition. You can also view the entire list by selecting it from the menu bar.