A portable application (portable app) is a computer software program that is able to run independently without the need to install files to the system it is run upon. They are commonly used on a removable storage device such as a CD, USB flash drive, flash card, or floppy disk. Portable apps should not be confused with software portability where software allows its source code to be compiled for different computing platforms. Portable applications can be run on any computer system with which they are compatible but typically require a specific operating system such as Microsoft Windows XP or above, certain version of a Linux distro, etc.
Portable software is typically designed to be able to store its configuration information and data on the storage media containing its program files.