Khali ("empty") marks the unstressed portion of a tala, shown with a wave instead of a clap and written 0. It is not silence: the theka continues, but open bayan strokes give way to closed ones — Dha becomes Ta, Dhin becomes Tin.
Khali is a navigation aid as much as a sound. In a 16-beat cycle its wave on matra 9 tells player and listener exactly where they are, which is why khali placement is the fastest way to tell same-length talas apart. Keeping the bayan genuinely quiet through khali, then reopening it cleanly, is a core theka discipline.