Here are some useful terms to help understand what people are talking about:

LP = Location Points

AC = Ancient Coins

VM = Vanguard Marks

CM = Clan Marks

Infs = Infusions (see infusion and materials guide to learn more)

EO = Earth Only (see triumphs to learn more)

HM = Hard Mode

DR = Decode Rank

UW = Underworld

NA = New Agora

MO = Mount Olympus

FS = firestream (the dev)

VG = Vanguards

PE = Public Events

ST = Super Titan

TR = Titan Rush

GT = God Tier (upcoming endgame update)

D = Deathless (using in combination with HM and EO commonly to signify getting multiple triumphs in one run)

VQM = Vanguard Quartermaster

LB = Leaderboard