Electrical Code…
Operation at a substantially constant load for an indefinitely long time.
Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.
Intermittent operation in which the load conditions are regularly recurrent.
Operation at a substantially constant load for a short and definite, specified time.
Operation at loads, and for intervals of time, both of which may be subject to wide variation.
(National Electrical Code® 100-1)