An application bundle is a collection of software that is distributed as a single package. Bundling applications together is a popular technique used by software vendors to attract customers, who may be interested in only one of the programs in the package but are willing to pay for or accept the entire bundle for the perceived value of having all the included software.
The software included in a bundle is up to the discretion of the software vendor: it can be a program with a separate installer or uninstaller; an operating system and a basic suite of programs; a game and related components; and so on. In more ambiguous cases, the bundled applications may be potentially unwanted applications (PUAs) or Unwanted Applications (UA).
Some application bundles present all the included software very transparently to the user, and clearly allow them to choose which programs they wish to install. For example, they prominently display an End User License Agreement (EULA), don't require the user to install all the included programs if they only want one application in the bundle, and cause no problems during the installation process.
Other application bundles are less transparent. For example, the user may only be notified about the presence of additional programs by a small, easily overlooked checkbox in the installation process. Alternatively, the installation process may be designed in such a way that when they try to install one application, the user is required to agree to install all the other bundled programs.
If you are aware of and agree to the terms and conditions for the other software included in the bundle, you may choose to proceed with installing all the programs. If you do not, you may opt to install only the desired program, if that is permitted during the installation process.