Minecraft wiki entry for Exploration_Update, associated text: 3 new splashes.
2 new villager professions:
Cartographer
Nitwit
2 new particles: spit and totem.
3 new NBT tags:
LocName, CustomPotionColor and ColorMap.
2 new gamerules: doWeatherCycle and maxEntityCramming.
1 new command: /locate.
Curse enchantments.
4 new mobs:
Vindicators, Evokers, Vexes, and Llamas.
1 new generated structure: Woodland Mansion.
2 new blocks: Observer and Shulker Box.
8 new spawn eggs.
4 new items:
Shulker Shell, Totem of Undying, and the two Explorer Maps.