Definition:-

• Failure to fulfill an obligation, especially to repay a loan or appear in a court of law. (noun)
• A preselected option adopted by a computer program or other mechanism when no alternative is specified by the user or programmer. (noun)
• Fail to fulfill an obligation, especially to repay a loan or to appear in a court of law. (intransitive verb)
• (of a computer program or other mechanism) revert automatically to (a preselected option) (intransitive verb)