XML is a way of writing information in a plain text file so that both a computer and a person can see what each piece of the information IS, not just what it says. You wrap each piece in a tag: <price>250</price> says "this 250 is a price". Tags can sit inside other tags, so a whole thing with parts — a book with a title, an author, a year — keeps its shape. That shape is the point. Because the labels travel with the data, one program can send a file to a completely different program, on a different computer, written by different people, and the second one can still find the price, because it just looks for the price tag. Before this, programs each had their own private file format and could not read each other's. The letters stand for Extensible Markup Language. "Markup" means the tags added around the text; "extensible" means you invent your own tag names — XML does not come with a list of tags, it only tells you the rules for writing them. That is the difference from HTML, which has a fixed set of tags (p, div, a) for one job, showing pages in a browser. It is a countable-ish technical noun, mostly used without an article: "the settings are in XML", "we export XML", "an XML file", "XML format". You will meet it in app settings files, in older company systems, in ebooks (EPUB), in office documents (.docx is XML inside a zip), and in RSS feeds. In new work people often choose JSON instead, which is shorter and easier to read, so XML now feels a bit old-fashioned — but it is everywhere in systems that already exist, and it is not going away.