Horizontal thoughts are looking to elaborate, looking for reference points, what’s right, what’s wrong, gossip... it’s conversation like “What do you think about what I think about what you’re thinking I’m thinking?” Vertical thoughts are looking at that kind of structure and by training the mind to sit still and watch what moves eventually starting to recognize that the thoughts are just showing up in open space. They begin to transcend the self-centered mind. When that occurs the thoughts actually come and help you in your life.

https://www.youtube.com/watch?v=HMAkTEf_n4I