Wiktionary
selenous acid
n. (context chemistry English) The oxoacid H2SeO3; the selenium analogue of sulfurous acid.
Wikipedia
Selenous acid
Selenous acid (or selenious acid) is the chemical compound with the formula HSeO. Structurally, it is more accurately described by (HO)SeO. It is the principal oxoacid of selenium; the other being selenic acid.