Sruti
The pitch reference that anchors a performance.
In everyday practice, sruti refers to the chosen pitch of Sa and the drone that helps maintain it. A singer chooses a comfortable tonic; accompanying instruments tune to that reference.
Listen against Sa
Sound a steady Sa, then sing or play another svara and return. Listen to its relationship with the drone, rather than treating its note name as an absolute keyboard pitch.
In music theory, sruti also refers to subtle pitch distinctions. The traditional discussion of 22 srutis should not be read as 22 equal steps of a keyboard.