A portable application (portable app) is a software product designed to be easily moved from one computing environment to another. They include portable versions of regular applications – such as browsers, for example – as well as specialized apps designed to enhance mobile computing. Portable apps are typically open source and either free, low-cost or donation-funded.
Portable apps are usually stored on USB drives but can be stored on some other flash media. A portable app may also be uploaded to a cloud storage service, such as Dropbox or Google Drive, and accessed online. In either case, portable apps can be used on any compatible device, wherever the user is.
A portable app is not installed and as a rule, does not put associated files and configuration information on the host device but stores all application files and data together. Because files and data are self-contained, portable apps run independently of the host operating system (OS).
Nevertheless, portable apps are created for compatibility with specific operating systems. The portability in portable apps refers to the way they can be physically carried from one place to another, not interoperability among different operating systems. Software portability (a different concept) involves software that is written so that the source code can be compiled for different platforms.