What is "staling"

Stale \Stale\, v. t. [imp. & p. p. Staled (st[=a]ld); p. pr. & vb. n. Staling.] To make vapid or tasteless; to destroy the life, beauty, or use of; to wear out.

Age can not wither her, nor custom stale Her infinite variety.
--Shak.

n. (label en food industry) The process whereby bread goes stale. vb. (present participle of stale English)

Staling, or "going stale", is a chemical and physical process in bread and other foods that reduces their palatability. Stale bread is dry and leathery.