A more thorough explanation:

Defectus (di-fek-təs), n. [from Latin deficere “to be deficient”] refers to a defect or a deficiency in something.

• A car with a defect in the engine may not run properly.
• A deficiency in a student's knowledge of a subject may result in a poor grade.
• A product with a defect may need to be recalled by the manufacturer.

The examples illustrate how defectus refers to a problem or lack of something. In the first example, the defect in the car's engine is causing it to not function properly. In the second example, the deficiency in the student's knowledge is resulting in a poor grade. In the third example, the defect in the product may cause harm to the user and require the manufacturer to take action.