Type System (Typographic Hierarchy)
A type system defines which typefaces a company uses and in what graded sizes, weights, line heights and spacing they are applied. It ensures that headings, body text, captions and buttons look the same everywhere and that the reading order stays clear.
In practice
Two typefaces are almost always enough, and one well-built family with several weights often suffices. Hierarchy matters more than the choice: if heading, subheading and body text are clearly distinguishable, even a plain typeface looks professional. The most common mistake is body text set too small with lines packed too tightly; legibility on a phone beats any design ambition. Variable fonts, described in the OpenType specification as font variations, deliver many weights in one file and can reduce loading time. Also check that the typeface contains the umlauts, the eszett and the special characters you actually need.