What is fault-masking?

Fault masking is a technique wherein one defect prevents the detection of another. there are many features that may have defects but remain hidden until these feature are utilized. For eg. In case of login page, developer has provided option to log in with email address and mobile number, until user logs in with valid credentials, the defect as below, wherein forgot password when registered mobile number is entered OTP is not received on mobile (unhandled task by developer), remains un noticed. This is known as fault masking.