It is derived from the Greek word ἔκτος (éktos), meaning "outside" or "external."
Here are some examples of words using the prefix ecto-:
* Ectoderm: The outermost layer of cells in an embryo.
* Ectoparasite: A parasite that lives on the outside of its host.
* Ectothermic: Referring to animals that rely on external sources of heat to regulate their body temperature.
* Ectotrophic: A type of mycorrhizae (fungal association with plant roots) where the fungus grows outside the root cells.
Therefore, "ecto-" helps us understand that something is located or related to the outside or exterior of a structure, organism, or system.