The slide master is an element of the design template (design template: A file that contains the styles in a presentation, including the type and size of bullets and fonts; placeholder sizes and positions; background design and fill color schemes; and a slide master and optional title master.) that stores information about the template, including font styles, placeholder (placeholders: Boxes with dotted or hatch-marked borders that are part of most slide layouts. These boxes hold title and body text or objects such as charts, tables, and pictures.) sizes and positions, background design, and color schemes (color scheme: A set of eight balanced colors that you can apply to slides, notes pages, or audience handouts. A color scheme consists of a background color, a color for lines and text, and six other colors selected to make slides easy to read.).

Font styles for title, body, and footer text
Placeholder positions for text and objects
Bullet styles
Background design and color scheme
The slide master's purpose is to let you make a global change — such as replacing the font style — and have that change reflected on all the slides in your presentation.
You would typically go to the slide master to do the following:
- Change the font or bullets
- Insert art — such as a logo — that you want to appear on multiple slides
- Change placeholder positions, size, and formatting
To see the slide master, you display master view. You can make changes to the slide master just as you would change any slide, except remember that the text on the master is only for styling; actual slide text, such as titles and lists, should be typed on the slide in normal view or, for headers and footers, in the Header and Footer dialog box.
When you change the slide master, changes you have made to individual slides are preserved.
A slide master is added to your presentation when you apply a design template. Usually, the template also contains a title master, on which you can make changes that apply to slides with a Title Slide
layout (layout: The arrangement of elements, such as title and subtitle text, lists, pictures, tables, charts, AutoShapes, and movies, on a slide.).
Making changes to multiple slide masters
If you apply more than one design template to your presentation, you will have multiple slide masters: one for each design template you've applied. So, if you want to make a change throughout your presentation, you need to change each slide master or pair of masters (depending on whether you're using the title master, too).

First slide-title master pair, with art applied to the title master. To add this art to all other slides in the presentation, you would add it to the slide master in this pair and to the second slide-title master pair.
Second slide-title master pair.
To facilitate your work with multiple masters, Microsoft PowerPoint includes commands for inserting, deleting, renaming, duplicating, and preserving masters. When you preserve a master, you protect it from being deleted automatically in certain cases by PowerPoint.