Applications are the tools people use to do useful things with computers, such as word processing, spreadsheets, presentations, databases etc.
In some areas these applications are dominated by a single program, which – due to its dominance in that area benefits from a feedback loop – since it is so widely used – is the only one which is taught, and hence the only option people know of.
This does not result in a healthy marketplace.
For the Microsoft Desktop Applications there are alternatives which perform the same functions, and trying out these alternatives improve understanding of the application, and even make transition from, for example one version of Word to the next easier.