The National Electrical Code draws a line at three hours: a load expected to run at its maximum current that long or longer is a continuous load. Lighting, EV charging, and water heating are the classic examples — equipment that holds its full draw for extended stretches rather than cycling. The distinction exists because sustained current heats conductors and breakers differently than intermittent current does.
The consequence is the 125% rule of NEC 210.19(A) and 215.2(A): conductors and standard overcurrent devices must be sized for 125% of the continuous load plus 100% of the non-continuous load. A 40 A continuous load therefore needs a conductor good for 1.25 × 40 = 50 A — walking NEC Table 310.16 upward, 14, 12, and 10 AWG copper all fall short and 8 AWG at 75 °C carries exactly 50 A, landing the circuit at 100% utilization.
The multiplier stacks with everything else the code throws at a conductor: the 125% factor sets the required ampacity, and the ambient-temperature correction, bundling adjustment, and termination temperature limits then decide which conductor actually delivers it. It is one of the four standard modifiers that turn the raw 310.16 table value into a usable number.