Portable applications are software programs designed to run directly from a removable storage device, such as a USB flash drive, without needing to be installed on a computer. This allows users to carry their favorite applications and settings with them, making it easy to use them on different computers without leaving a trace behind. These applications are often lightweight and do not modify the host system's registry or files, ensuring a clean and hassle-free experience. Popular examples of portable applications include web browsers like Mozilla Firefox and productivity tools like LibreOffice, which provide flexibility and convenience for users on the go.