Medical Definition of alga
plural algae \ˈal-(ˌ)jē\play also algas
: a plant or plantlike organism of any of several phyla, divisions, or classes of chiefly aquatic usually chlorophyll-containing nonvascular organisms of polyphyletic origin that usually include the green, yellow-green, brown, and red algae in the eukaryotes and especially formerly included the cyanobacteria in the prokaryotes
Seen and Heard
What made you want to look up alga? Please tell us where you read or heard it (including the quote, if possible).