below standard or less than adequate: substandard housing conditions.
2.
noting or pertaining to a dialect or variety of a language or a feature of usage that is often considered by others to mark its user as uneducated; nonstandard.
3.
Insurance.
a.
not measuring up to an insurer's regular standards in undertaking risks: a substandard risk.
b.
pertaining to insurance written to cover substandard risks.