TIMEWARPED

These pieces are an exceptionally higher item level than normal drops, but do not drop with terts or sockets. These can only drop on TIMEWALKING difficulty, and are only accessible during their related Timewalking rotation week.

SOCKETED

These pieces are consistent, fine without the suggested procs, and can be farmed for repeatedly. Similar pieces will work too, so don't worry too much if it's not the exact piece listed. These can only drop on NORMAL difficulty.

APEXIS

Drops from specific rares in Draenor, called Apexis Rares, can socket on any slot. They can also proc with terts. These can be farmed once a day without help from outside toons, and can be traded if first chance. List here.

TANAAN

Drops from the zone Tanaan Jungle are item level 44, can have higher stats and can socket on any slot. Either have a high level trade it down to you or loot it in Lorewalking.
IGNORE BALEFUL GEAR TOKENS.

WILD CARD!

Pieces that are only exceptional if certain qualifiers are met, and/or cannot be easily farmed for due to being often once-per-toon or other obstacles. The origin of these is usually quests, rares, or random procs on drops.