A slide master is the top slide in a hierarchy of slides that stores information about the theme and slide layouts of a presentation, including the background, color, fonts, effects, placeholder sizes, and positioning.
Every presentation contains at least one slide master. The key benefit to modifying and using slide masters is that you can make universal style changes to every slide in your presentation, including ones added later to the presentation. When you use a slide master, you save time because you don't have to type the same information on more than one slide. The slide master especially comes in handy when you have extremely long presentations with lots of slides.
Because slide masters affect the look of your entire presentation, when you create and edit a slide master or corresponding layouts, you work in Slide Master view.
1. A slide master in Slide Master view
2. Slide layouts associated with the slide master
When you modify one or more of the layouts beneath a slide master, you are essentially modifying the slide master. Each slide layout, is set up differently, yet all layouts that are associated with a given slide master contain the same theme (color scheme, fonts, and effects).
The following image shows a single slide master with the Flow theme applied, and two (different) supporting layouts. Notice how each of the two layouts shown portray a different version of the Flow theme — using the same color scheme, but in a different arrangement. Also, each layout provides text boxes and footers in different locations on the slide, and different font sizes in the various text boxes.
When you want your presentation to contain two or more different styles or themes (such as backgrounds, color schemes, fonts, and effects), you need to insert a slide master for each different theme. In the image that follows, there are two slide masters as you would see them in Slide Master view. Each slide master has a different theme applied to it.
When you go to Slide Master view, you'll see that there are several default layouts associated with any given slide master. Most likely, you will not use all of the layouts provided. You choose from the available layouts, the ones that work best to display your information .
You can create a presentation that contains one or more slide masters, and then save it as a PowerPoint Template (.potx or .pot) file and then use it to create other presentations. This file includes everything a slide master contains, and more.
Important: It is a good idea to create a slide master before you start to build individual slides, rather than after. When you create the slide master first, all of the slides that you add to your presentation are based on that slide master and the associated layouts. When you start making changes, make them on the slide master.
Also, if you create a slide master after you build individual slides, some of the items on the slides may not conform to the slide master design. You can override some of the slide master customizations on individual slides by using the background and text formatting features, but others (such as footers and logos) can be modified only in Slide Master view.