What is the meaning of Alga?

Any of many aquatic photosynthetic organisms, including the seaweeds, whose size ranges from a single cell to giant kelps and whose biochemistry and forms are very diverse, some being eukaryotic.

Something of little worth.

alga (any of many aquatic photosynthetic organisms)

alga (any of many aquatic photosynthetic organisms similar to plants or bacteria)

seaweed (any marine plant)

Source: wiktionary.org

See also