With Heart of Thorns coming, Anet is giving us bits and pieces of info on some of the amazing things to come. Today they released a wonderful blog about Masteries. you can read it here: https://www.guildwars2.com/en/news/reimagining-progression-the-mastery-system/
It looks like there will be 5 types of masteries to train in:
Master Lore: Attunement with new ally races can be trained to understand their language, unlocking secret locations and access to battle techniques that can weaken your shared enemies.
Master Legends: Train in legendary crafting to learn to create all existing legendary weapon precursors and new legendary weapon precursors introduced with Heart of Thorns.
Master Exploration: Mastering jungle movement will unlock the ability to hang glide to previously unreachable locations as well as the ability to use special mushrooms to traverse the Heart of Maguuma faster.
Master Combat: The Heart of Maguuma will be home to some of the most challenging combat in Guild Wars 2, and Masteries will give you the tools you need to excel in these fights. Hunt new enemies, master abilities to defeat champions, and become more deadly against the new creatures waiting in the jungle.
Master Fractals: Uncover new depths in the Fractals of the Mists to gain powerful new abilities to overcome difficult fractal challenges, garner greater rewards, and unlock more powerful infusions.
The Question is... Which one will you start out training in?