Bioform

A bioform is a term for any living creature. The term is heavily used throughout lore in the Metroid Prime series, and has never been used in any of the 2D games. The term has also been applied to individual characters, such as Samus Aran, who is referred to as "Bioform Samus Aran" in at least two Space Pirate communiques. Metroid Prime: Federation Force also uses an alternative name for creatures, xenoform.

The vast majority of bioforms encountered in the Metroid series are hostile for a number of reasons. This includes telepathic control (such as by Mother Brain, at least in the original Metroid), a malevolent nature (such as the Ing), or the bioform is merely defending itself. Some bioforms, particularly in the Prime series and Metroid: Other M have been cybernetically enhanced.

Trivia

 * In Metroid Prime, Ridley is named Geoform 187 in scans. This suggests that he is not a natural bioform, at least not with his cybernetic enhancements.