Page files are a type of temporary storage used to extend the available RAM on the computer. The operating system uses page files to temporarily move portions of RAM which is not frequently accessed so that that part of the RAM can be made available for
additional processing.
Page file is not something specific to SQL Server, but more like an overall windows operating system level configuration to maintain the correct health and balancing of the resources.
I would recommend reading this
KB article which provides an overview of page files.
My Blog