Markdown is a special syntax that allows quick and easy styling of text as well as including images, links and more. Instead of selecting text styles for a cell, this allows you to define for example a headline like this:
# Hello world
This could be used in several places e.g. in Spreadsheet cells, In form elements, Integrator Description etc.
There are some open source libraries that make this quite easy by automatically translating Markdown into HTML.
