An imperfection or deficiency in a project component where that component does not meet its requirements or specifications and needs to be either repaired or replaced.
Merriam-Webster Online Dictionarydefect (noun)
a) an imperfection that impairs worth or utility - shortcoming the grave defects in our foreign policy
b) an imperfection (as a vacancy or an unlike atom) in a crystal lattice
Latin a lack of something necessary for completeness, adequacy, or perfection - deficiency a hearing defect
to forsake one cause, party, or nation for another often because of a change in ideology
to leave one situation (as a job) often to go over to a rival - the reporter defected to another network