This adverb borrowed from Latin means “in the broad sense” — its counterpart is “sensu stricto,” which means “strictly speaking.” Either of these adverbs can be used in prose, but they’re also used by taxonomists (scientists concerned with the classification of biological organisms) to discuss members of a taxon (category). “Sensu lato” refers in a broad sense to all members of a taxon, and “sensu stricto” is used to refer to a more specific subset.