Question: What is sajdah sahw?

Answer:

Sujoodus-sahw means the performance of two additional Sujood (prostrations) in order to compensate for a defect in the Musalli’s performance of Salaat, The defect or fault, however, must have been committed by error – by mistake, and not intentionally. If the defect was caused intentionally, no Sujoodus-Sahw can be performed.