In computer terminology, the word "default" refers to the response a computer is programmed to have unless the user instructs it to do something different. Default settings can be programmed by the user or by the company that manufactures the computer or software being used.
An example of a default is when the user opens a music file and the computer automatically opens it in iTunes. There may be other choices to play music files, such as Windows Media Player, but the computer is programmed to attempt to open this type of file in iTunes first as its default software option. Different types of files may have different default programs. Default responses can generally be changed in the settings menu for the computer or program.