Markups are also ubiquitous in the world of computers. They are used by word processors to specify formatting and layout, by communications programs to express the meaning of data sent over the wires, by database applications that must associate meaning and relationships with the data they serve, and by multimedia processing programs which must express meta-data about images or sound. HTML is one of the more famous computer markup systems. HTML defines a set of tags that associate formatting rules with bits of text. Actually, though HTML is often called a programming language it is really not.
Programming languages are 'Turing-complete', or 'computable'.
That is, programming languages can be used to compute something such as the square root of pi or some other such task. Typically programming languages use conditional branches and loops and operate on data contained in abstract data structures. HTML is much easier than all of that. HTML is simply a 'markup language' used to define a logical structure rather than compute anything. It is sort've a semantic issue, but it is one which you should officially be aware of.