Vertical generally refers to the comparison of the same thing in different periods. In the academic system, the single-track system is vertical, which refers to the division by age stage.
Supplement: On the question of who has more advantages, your horizontal direction here should refer to the academic system of separate disciplines, the combination of single-track system and dual-track system. For example, from primary school to high school, the single-track system is vertical, and the following disciplines and majors are double-track and horizontal, that is, professional learning. The above is just an analogy. The actual situation is more complicated, but it can be basically understood. You can take online courses, such as massive open online courses of China University and Tang Xue Online. The following links are basic introductions to the three types of educational systems. (Please register first) Web link
Personal views and understanding, hope to adopt.