Definition - What does Helper Application mean?
A helper application is any application that handles files received by a Web browser. It is non-native and unviewable by the browser. A browser invokes a helper application through a prebuilt component in the browser's stored list of applications.
Techopedia explains Helper Application
For example, a standard browser is unable to directly play a MP3 file. If a browser receives or downloads a MP3 file, it will access its list of helper applications to locate a compatible MP3 application, such as Windows Media Player. If there is no related application, the browser may recommend finding a match by searching the computer and/or the Internet.
Moreover, a user may manually customize a browser's list of helper applications, either to swap an existing helper application or add a newer helper application for different file extensions.