Apparently there is some confusion on E2 about terms for cattle, including "heifer", which Webby does not fully alleviate.
A heifer is a young cow, yes, where cow means specifically a female of the cattle species (genus Bos) and also one which has never borne a calf. Heifers are categorized separately in livestock trading, for example.
According to Numbers 19, a red heifer is required for purification and dedication of a high temple. Such an animal, which cannot be impure by so much as six discolored hairs, would be a literal holy cow.