What is rsoh in sdh?

Regenerator Section OverHead -

* 9 rows by 270 columns * Regenerator OH lives in first 3 rows * Row1: A1 A1 A1 A2 A2 A2 J0 * Row2: B1 r r E1 r r F1 * Row3: D1 r r D2 r r D3

PS