Aroha (ascending) and avaroha (descending) are paired concepts that describe how a raag traverses its octave. A raag is not defined by its set of notes alone — it is defined by how the artist must approach those notes when going up and coming down. Two raags can share the same seven notes (same thaat) and still be entirely different because their aroha-avaroha patterns differ.
In some raags, aroha and avaroha use exactly the same notes. In many others, they differ. Raag Bhupali uses only five notes (Sa Re Ga Pa Dha) in both directions — pentatonic, symmetric. Raag Bilaskhani Todi has a different note set going up than coming down. Raag Hamsadhwani omits certain notes entirely in descent, creating a distinctive falling shape.
The aroha-avaroha pattern dictates much of what feels "correct" in a raag performance. Going against the pattern — using a forbidden note, or approaching a note from the wrong direction — immediately sounds wrong to a trained listener, even if the same note belongs to the raag in the other direction. This is why two raags using identical notes can sound completely different.
Aroha-avaroha is one of the first things a student learns when studying a new raag. Before any phrase, before any taan, the student must internalise: how do I go up in this raag? How do I come down? That movement, repeated thousands of times, becomes muscle memory — the foundation on which everything else rests.