Exposure value (Ev) is a measure of the light exposed in a photo, combining exposure time and aperture.
It uses fancy math to facilitate the choice of exposure : opening of the aperture can be linked (mechanically or electronically) to the lowering of the exposure time.
It’s equal to 1 stop, aka 1 step in the settings of exposure time, and aperture on cameras.
It follows a non-linear law (power law ?)
This was useful in mechanical film cameras to change setting easily without having to find the correct exposure every time.
The EV is used in camera specs & lingo.
For example, DxOmark characterizes dynamic range as Ev plotted as a function of ISO.