1. A small, usually single-celled reproductive body that is resistant to adverse environmental conditions and is capable of growing into a new organism, produced especially by certain fungi, algae, protozoans, and nonseedbearing plants such as mosses and ferns.

2. A megaspore or microspore.

3. A dormant nonreproductive body formed by certain bacteria often in response to a lack of nutrients, and characteristically being highly resistant to heat, desiccation, and destruction by chemicals or enzymes.