Richard Rutter writes about variable fonts. So many variations from a single file!
In October 2016, version 1.8 of OpenType was released, and with it an extensive new technology: OpenType Font Variations. More commonly known as variable fonts, the technology enables a single font file to behave like multiple fonts. This is done by defining variations within the font, which are interpolated along one or more axes. Two of these axes might be width and weight, but the type designer can define many others too.