An example of an extension is adding a second story to a single story house.
An example of an extension is line two on a business line.
An example of an extension is someone getting an extra fifteen days to pay their electric bill.
The wire has an extension of 50 feet.
In most operating systems, filenames having the extension .EXE are executable files.
An extension to a factory.
Extension ladder, extension cord.
Files with the .txt extension usually contain text.
The extension of the subway into the suburbs.