(This list does not include weapons or perks or other technical terms)
[u][b]NF[/b][/u] - [i]Nighfall[/i], originally an alteration of your run of the mill strike, it was stacked with modifiers including one that put you back into orbit upon a Fireteam wipe, all in the hope to receive some of the best rewards in the game, including an xp boost. Since year 2, it's just been a glorified heroic strike with mediocre rewards and isn't considered worth anyone's time.
[u][b]VoG[/b][/u] - [i]Vault of Glass[/i], raid featured in Vanilla Destiny
[b][u]IB[/u][/b] - [i]Iron Banner[/i], PVP event. Originally exclusive to Control. Now encompasses Clash and occasionally Rift.
[b][u]TDB[/u][/b] - [i]The Dark Below[/i], Destiny's first expansion. Dark times indeed.
[b][u]CE[/u][/b] - [i]Crota's End[/i], TDB's raid, notorious for being able to be soloed.
[b][u]HoW[/u][/b] - [i]House of Wolves[/i], Destiny's 2nd expansion. Introduced gear ascension.
[b][u]PoE[/u][/b] - [i]Prison of Elders[/i], Destiny's first Arena, introduced in HoW, it became tedious very quickly. Dismantle mines, yeesss?
[b][u]ToO[/u][/b] - [i]Trials of Osiris[/i], long awaited PVP event that came along in HoW along with the introduction of Elimination. Do you have what it takes to get to the Lighthouse?
[b][u]MoT[/u][/b] - [i]Moments of Triumph[/i], yearly activity held to see if you as a player managed to "git gud" and stay good.
[b][u]TTK[/u][/b] - [i]The Taken King[/i], Destiny's first DLC that seemed like a DLC.
[b][u]CoO[/u][/b] - [i]Court of Oryx[/i], a PVE activity that serves as a spiritual successor to PoE. Engrams galore.
[b][u]KF[/u][/b] - [i]King's Fall[/i], TTK's raid. Infamous for being long, tedious, and giving you everything but what you needed to hit max light. Gotta have those moldering shards.
[b][u]FotL[/u][/b] - [i]Festival of the Lost[/i], Halloween event created solely to take our money. Unless you like collecting candy. What are you, 14? Wait...
[b][u]SRL[/u][/b] - [i]Sparrow Racing League[/i], also created to take our money, this event was actually fun, they removed it for seemingly no reason. Some argue racing doesn't belong in a shooter. But apparently dancing does.
[b][u]CD[/u][/b] - [i]Crimson Doubles[/i], Bungie's third attempt to satisfy our hunger in the content drop. This Valentines Day event was actually created by High Moon Studios and not Bungie.
[b][u]CotE[/u][/b] - [i]Challenge of the Elders[/i], a large portion of the community decided to ignore the "the" and shorten it to the easier [u][b]CoE[/b][/u], CotE/CoE serves as an upgraded and revamped PoE added during the April update.
[b][u]RoI[/u][/b] - [i]Rise of Iron[/i], Destiny's much awaited 2nd full-scale DLC. The fact that I and lower case L's look alike make this acronym feel awkward.
[b][u]AF[/u][/b] - [i]Archon's Forge[/i], Destiny 2nd Arena, being introduced in RoI, much is unknown about it, but it's lit.
[b][u]WotM[/u][/b] - [i]Wrath of the Machine[/i], RoI's Raid, like most RoI content, not much is known about it other than the fact the raid gear looks a bit strange.
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Nice list, just so you know TTK can also mean "time to kill"