planefags pls help

At the behest of a fren, I'm looking for more information about this. What do the acronyms mean (NM, AGL, FL), and what are the potential implications of what's being set forth here?

ThankQ!

(will repost next bread if nothing turns up here)

>South East Search and Rescue Associates

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> You might want to check your map and compass skills before Feb. 6-10, 2019. Why? The military who owns the GPS system is going to do some GPS jamming testing off the coast of Georgia on those dates. Serious degradation can occur at times over those days at or near ground level all the way to NW Georgia. For aviation users much further. Think of the horror when all the millennials can't find the nearest Starbucks.