Master pages give your presentation a consistent look by defining what fonts and other design elements are used. Impress uses two types of master pages:
Master Slide
Contains elements that appear on all slides. For example, you might want your company logo to appear in the same place on every slide. The slide master also determines the text formatting style for the heading and outline of every slide that uses that master page, as well as any information you want to appear in a header or footer.
Master Notes
Determines the formatting and appearance of the notes in your presentation.