Definition - What does Markup mean?
Markup is language in the form of code instructions where each code instruction is inserted in a markup-language-based file to tell the markup-based viewer software where to put this text or that graphic. Each written code affects the final look of a markup-language-based file, which includes text attributes, graphic positions and picture size. The most well-known markup languages include HTML, XML and XHTML.
Techopedia explains Markup
Although there are software packages that translate graphical and other object structures into markup code, a developer can also write the markup-based code himself. It is highly recommended that all Internet application developers learn markup language details, even if they are going to use a graphics-based editor to design their website. This is because graphics-based editors may not have the full functionality that is required, and there are applications that need manual editing like inserting code that links to other Web published components, such as the banners and ads used in affiliate programs.