v. To switch from one running computer program to another.
On a recent morning I was toiling away, when my PC began talking—not something I normally expect when I'm working in Microsoft Excel. I heard voices, then music. I Alt-Tabbed through my running apps until I came to the AIM client with my active buddy list. Running in the top of the window was a roughly 240-by-120 video of the trailer for a new Ben Affleck movie.
You know the feeling. You're typing along, and all of a sudden you have to look something up. Most word processors these days have adequate (even good) spell-checking dictionaries and thesauri. But if you need an encyclopedia or an atlas—or anything else that isn't built into the program itself, for that matter—switching over can be tedious at best. By the time you've Alt-Tabbed out to Program Manager, found the right icon, and brought that trusty multimedia encyclopedia to life, there's a 50-50 chance you've forgotten what you wanted to look up in the first place.
If Alt-Tabbing between programs produces hard disc activity, you may need to add one or two more megabytes or not load so many programs at once.