Something substandard is below standard — it's shoddy or inferior.

What is a meaning of substandard?

: deviating from or falling short of a standard or norm: such as. a : of a quality lower than that prescribed by law substandard housing. b : conforming to a pattern of linguistic usage existing within a speech community but not that of the prestige group in that community.

What is the synonym of inferior?

In this page you can discover 70 synonyms, antonyms, idiomatic expressions, and related words for inferior, like: lower, subordinate, deficient, mediocre, second-rate, subaltern, bum, underneath, under, assistant and low priority.