Adobe Photoshop Portable is an image editing application for the Windows and Macintosh operating systems. It is a version of the standard application which has been stripped of non-essential files to allow for the quickest possible peer-to-peer sharing and specifically with portable use in mind. It is not officially sanctioned by Adobe Systems, Inc., but rather user-engineered and generally shared free of cost via the Internet.
Photoshop, created by Adobe Systems, Inc., is arguably the most popular digital image editing application in the world. It is so popular and its capabilities so widely renowned that "Photoshop" has become a verb used to refer to digital image manipulation. Specifically, Photoshop is famous for its ability to allow users to take parts of one digital image, (for example, a person's face), and paste them believably into another image (such as on another person' body).
Adobe Photoshop Portable refers to a version of the program that has been stripped of its extraneous files. Applications generally contain many files are not necessary for the actual operation of the program. An example of these files would be help files. There are hundreds, sometimes thousands of text files in a given application's help file system. Stripping these out makes an application smaller in physical size, which makes it easier to share via the Internet and easier to store on portable storage devices.
The true appeal of a "portable" application is that it is engineered such that one can store it on a portable storage device such as a thumb drive and use it on multiple computers. It is built so that no additional system files are necessary; a user can simply plug a thumb drive into a computer at home or at work and run the "portable" application from the thumb drive.