The word ma'soom is often equated with the English word Infallible which means incapable of error. However, people who are described as ma'soom do not make errors or commit sins, but they have the ability to make errors and commit sins.

Many Muslims say the Prophets (PBUT) are masoom but the Shia also say the members of Ahlulbayt are masoom in addition to the Prophets. It is part of their 'aqueedah.