Colour space
A defined way of describing colours as sets of numbers, with stated limits and a reference white.
Also: colour model
A colour space is a map of colours. Each colour gets an address, usually three numbers, and the map states exactly what those numbers mean. A colour model, such as RGB, is the general scheme: so much red, green and blue. A colour space pins it down: which red, which green, which blue and which white. That is why the same three numbers can look different on two devices that assume different spaces. Common spaces include sRGB for the web, Display P3 for newer screens and Lab for measurement.