XML stands for extensible markup language. Markup means that XML's primary task is to give definition to text and symbols.
Language means that XML is a method of presenting information that has accepted rules and formats.
Markup languages were first developed by IBM and later implemented on a large scale within publishing companies. SGML is an ISO standard for defining document structures for the application of mark-up schemes. Publishing companies needed a means for marking up a document so that the words could be presented in a number of different ways. For example, a new product might require a detailed instruction manual and a beginner's guide. Both documents may require the publisher to re-use elements of the original.