This term describes the overall thickness of a stroke of the typeface in any font. One typeface can have various weights. The most common font weights are regular, bold and light. Font weight could vary from extremely light to extra thick, you should be aware that the names of the individual typefaces may vary depending on the designer or type foundry.
Usually, font-weight were separated into individual font files that you have to install. But with the introduction of the technology of variable fonts, all font weights are now build-in into one font file. Lovely and useful! Maths calculates the exact shape of the letterforms, allowing designers to create their bespoke combinations.