MacPorts is a system for compiling, installing, and managing free and open source software. MacPorts may be thought of as divided into two main parts: the infrastructure, known as MacPorts base, and the set of available ports. A MacPorts "port" is a set of specifications contained in a Portfile that defines an application, its characteristics, and any files or special instructions required to install it, so MacPorts may automatically fetch, patch, compile, and install ported software. MacPorts may also be used to pre-compile ported software into binaries that may be installed on remote computers. Binaries of ported software may be installed very quickly since the steps required to install ports from source code have all been performed in advance. MacPorts provides several major advantages over installing free and open source software manually. MacPorts automatically installs any required support software, known as "dependencies", for a given port. MacPorts confines ported software to a private "sandbox" that keeps it from intermingling with your operating system and its vendor-supplied software and prevents them from becoming corrupted. MacPorts provides automatic uninstalls and upgrades of ported software. MacPorts is developed on Mac OS X, though it is designed to be portable so it can work on other Unix-like systems, especially those descended from the Berkeley Software Distribution (BSD).

The MacPorts Guide uses some notational conventions to distinguish between terminal input/output, file text, and other special text types. Terminal I/O and file text. %% Commands to be typed into a terminal window. Command output to a terminal window. File text. Other special text types. A hyperlink: spontaneous combustion. A file: /var/log/system.log. A command: ifconfig.