There are three types of defects: Wrong, missing, and extra.

Wrong: These defects are occurred due to requirements have been implemented incorrectly.

Missing: It is used to specify the missing things, i.e., a specification was not implemented, or the requirement of the customer was not appropriately noted.

Extra: This is an extra facility incorporated into the product that was not given by the end customer. It is always a variance from the specification but may be an attribute that was desired by the customer. However, it is considered as a defect because of the variance from the user requirements.