A sub-standard service or product is unacceptable because it is below a required standard.
例句
Residents in general are poor and undereducated, and live in sub-standard housing.居民們普遍都很貧窮，受教育程度低，居住條件較差。
英漢詞典釋義
adj.
不夠標準的,在標準以下的
a substandard piece of merchandise一件不合標準的商品Too many families are still living in substandard housing.仍有太多家庭居住條件達不到標準。The reputation of the firm was blown upon for passing substandard products off as first-class merchandise.該公司因把次品當正品出售而名譽掃地。