Tier

From EQ2i, the EverQuest II wiki

When the word Tier is used in game, it is usually referring to the 10-level ranking of a thing. For instance Antonica has a level range of 10-22 (generally), and the harvest nodes in that zone yield harvestable raws of the 2nd ranking, hence it is a Tier 2 zone.

Tier is not an exact term, but in most things, such as which world channels you can chat in, it is from 0-9 of that decade. So, the Tier 2 channel is for users from 10-19. At 20 you gain access to the Tier 3 channel. Level 70 is therefore Tier 8.

In Tradeskilling it breaks down a little above level 50, stretching 1 level so that Tier 5 crafting is 40-50 and Tier 6 crafting is 51-60. This is a result of the way the level cap was raised.