An endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name 'endospore' is suggestive of a spore or seed-like form (endo means within), but it is not a true spore (i.e., not an offspring). It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in Gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall.