Downloader

A downloader is a program designed to retrieve and install additional files. Downloaders can be useful tools for consumers to automate upgrades of essential software such as operating system upgrades, browsers, anti-virus applications, anti-spyware tools, games and other useful or enjoyable applications of all kinds. Automated upgrades are useful for closing off security vulnerabilities in a timely way. Unauthorized downloaders are used by third parties to download potentially unwanted software without user notification or consent.

Source
Anti-Spyware Coalition Glossary.