I'm with ilusionist on this one, its very aliance dependant.
Some fleets are descriptive of what they do, for instance firewall fleets, or Armour HAC
Some are acronyms, some are just designed to strike fear with the name or to sound cool...
As for asking re:PL Hellcats are Pandemic Legion fleets, that much I can tell you:
Now my personal view I'm guessing they are desinged to be hit and run ships, hit hard move fast, but this is just speculation, it depends on the FC who created them, it may be a name after the FC who devised the tatic, it depends on a lot of things. PL tend to be very good tatical fighters, so I would expect them to have a very distinct role within their Flotilla.
Personally I prefer fleet names that tell me what I'm signing up for, nothing worse then signing up for a fleet called I don't know... "George and the AllStars" and turns out it's a pos bash :o( lol.
Sorry if it's a vauge answer but Fleet setups tend to be guarded secrets, and I wouldn't want to get anyone or myself in trouble by divulging anything sensetive even if it is in the name of education.
If anyone knows what PL’s HELLCATs are I’d be obliged…
HELLCATs, per a Eve News 24 comment, seem to be their standard fit (as evinced by their killmails) Abaddon).