Biochemical lifeform was a classification of species. Most living species in the known galaxy were of this nature.
When confronted with photonic lifeforms, Tuvok tried to explain to the explorers from the fifth dimension that the USS Voyager and her crew were biochemical lifeforms. The photonic lifeforms did not understand the term, and additionally did not think that he was real at all. (VOY: "Bride of Chaotica!")