A GN4 typography is a collection of various content formatting properties for the paper publishing. A typography is assigned to a title, and editions, pages and page layers are 'children' of a title.
For example, a typography contains the color table and the dashing definition, stretch/shrink parameters, words estimate, start/end shapes (directly i.e. as attributes of a typography object), and it is referenced by titles, fonts, font layouts, formats, style libraries, page geometries etc.
Thus, a typography defines the look and feel of the printed content, and - due to the XML part of styles - also the look and feel of the Web (or other channel) content. See also Multiple typographies.
You can create an arbitrary number of typographies. Typically, you need a separate typography for each publication (title), but more titles can share the same typography.
You associate a typography when creating a title. Therefore, to create a title, you need to have a typography already. Of course, you may also decide to use the Default typography, shipped with a new GN4 system and adapt it to your needs.
More about typographies
Disambiguation: for typographical properties, see Typography.
See also
Configuring Titles and Publications
How to find out to which typography/title is related your content?