Monolight
A self-contained studio flash with its power supply, controls and modelling lamp built into a single head.
Measured in
Ws (watt-seconds)
In depth
Because everything is in one housing, monolights are simple to set up and each is independently adjustable, but the weight sits at the top of the stand and every head needs its own mains or battery connection. Output is quoted in watt-seconds, though comparing brands on that number alone is unreliable because reflector efficiency varies enormously.
Examples in practice
A 500 Ws monolight in a softbox metering f/11 at 1.5 m has ample power to overpower a window's ambient light.