What is "resting spore"

Resting \Rest"ing\, a. & n. from Rest, v. t. & i.

Resting spore (Bot.), a spore in certain orders of alg[ae], which remains quiescent, retaining its vitality, for long periods of time.
--C. E. Bessey.

n. A spore, in certain orders of algae, which remains quiescent, retaining its vitality, for long periods of time.

A resting spore is a spore created by fungi which is thickly encysted (has a thick cell wall) in order to survive through stressful times, such as drought. It protects the spore from biotic ( microbial, fungal viral), as well as abiotic (wind, heat, xeric conditions) factors.