The Zandalar Tribe set is a type of item set. Each set consist of 5 pieces.
Three out of five items that form these sets are quest rewards. The quests require, among other things, token drops from bosses in Zul'Gurub. Reputation with the Zandalar Tribe is also required.
One is a Necklace, which can be upgraded throughout the reputation level to become the set piece at exalted.
The last piece is a trinket, which can be combined by the player from various drops in Zul'Gurub.
For details, refer to the set page.
This type of item set is sometimes also called "Tier 1.5".
The sets also contain a trinket, which is most unusual.