PowerPoint opens the master from View, Slide Master. The thumbnail at the head of the left-hand pane is the master itself; the ones listed under it are layout masters, one per arrangement, with names such as Title or Title and Content. Anything placed on the master, whether a font choice, a colour set, a footer or a logo, flows down to every layout, and each layout can then add or override its own placeholders. Microsoft advises editing the master and layouts before building individual slides, and notes a side benefit: elements set in Slide Master view cannot be deleted by accident by colleagues working in Normal view.
- Master: one per design, holding what every slide shares.
- Layouts: children of the master, each defining where title, text, picture and chart placeholders sit.
- Slides: built from a layout; typed content fills the placeholders and inherits their formatting.
- Several masters: a single file can carry more than one, each with its own layouts, which is how one deck uses two themes.
Google Slides and the theme
Google Slides reaches the same machinery through Slide, Edit theme, where the theme's colours and other shared settings are changed for the whole presentation at once. Google describes a theme as a preset group of colours, fonts, background and layouts, and that list matches, item for item, what PowerPoint keeps in its master. The discipline is shared too: change the theme, not the slides.
The same idea elsewhere
The same principle underpins a design system on the web and a web template for a site; a master is that idea shrunk to one file. When several people edit a deck at once through co-authoring, one person owning the master avoids a tug of war over fonts. The presentations topic puts masters and layouts first among the skills a deck needs.