Definitions for "cyanobacteria"
any of a group of photosynthetic autotrophic prokaryotic microorganisms possessing characteristics of both bacteria and plants. When classed as bacteria, they are assigned to the Cyanobacteria; when classed as plants, they are assigned to the Cyanophyta. They were earlier named blue-green algae, a term less used now in technical discussions. Since the chlorophyll within the cyanobacteria is diffused throughout the cell, rather than being contained in chloroplasts, they are no longer thought of as true plants.
Unicellular, photosynthetic (photo-autotroph) prokaryote (in the Kingdom Monera). Formerly known as blue-green algae. It contains chlorophyll a but not chloroplast. They reproduce by fission and never sexually.
Cyanobacteria is commonly referred to as red slime algae by hobbyists although it is not really an algae; it is a bacterium. Poor water quality with excessive nutrients is the usual causes. To combat cyanobacteria, perform frequent water changes, siphon out detritus, and if you have a salt-water aquarium, use a good protein skimmer.