The Multimedia communication: Multimedia is a way to convey messages (see the definition of Communication Science) that implements various communication techniques/technologies/media (i. e., ways of communicating), such as audio, images, text, movies, weblinks (and then we'll talk about iper-multimedia), algorithms, and so on. See also the term multimedia on Wikipedia.
Human beings are systems which exchange information in the form of messages to communicate in the above sense; this for the porpouse of learning (i. e., increase their knowledge; i. e., switch from one mental state to a better state). Man has always transmitted knowledge since prehistoric times and this transmission was through the media that they have gradually refined. In these terms it is clear that the term "communicate" means to "transmit knowledge." The first mean of communication that has been "invented" is the word or sound in general. These things are so primitive that even animals use them to communicate. Then it came the mean of communicating through images. Consider, for example, that prehistoric man who depicted on the walls of the cave, the animals he saw. With the advent of history, it was invented the communication medium of writing. Indeed, one can say that the beginning of the historical era has been characterized by the invention of writing. We can say that the first example of multimedia was the invention of a picture book in which communication was simultaneously both through writing and pictures. The word, music, writing and images have gone increasingly refining as communication media, but they were basically the only ways to communicate until the end of the eighteen hundreds when it was discovered the movie (= moving images) first silent and then sound. Both silent and sound movies are examples of multimedia: in the first communication is done using moving images, writing for the dialogues, and the music that served as a soundtrack played independently by a pianist (consider, for example the comedies of the early nineteen hundreds by Charlie Chaplin, Buster Keaton, Stan Laurel e Oliver Hardy, and so on). In the second case, communication is done using moving images, the words and music. Note that these means of conventional communication media exist because the five senses make "the human being a multimedia machine" when it receives messages.
We have said that the communication techniques are many. Nowdays, many of these techniques have a formal language (= language interpretable by a machine) representation which eventually results in a binary files. In particular, say, the Dante's "Divine Comedy" may be represented/encoded by the html formal language (see for example the Divine Comedy on wikisource.org) and its encoding may consist of one or more binary files. This implies that many communication techniques can be implemented with the machines via the automatic communication and, even more, through the automatic communication it is very simple and efficient to integrate various communication techniques and implement a multimedia communication (this site is a simple example of this).
I would now like to focus on two ways to communicate that with the advent of the automatic communication have had a great importance especially in the Web.
The Interactive communication: A communication between two entities A and B (whether they be human beings or machines) is interactive when A communicates something to B and B, based on this, communicates something else to A and, according to the latter thing, A communicates still something else to B, and so on. Note that, if B is a machine necessarily there is a program running on B that creates an interactive environment (with automatic responses); and this is another example of communication via algorithms. For example, whenever a Web page creates an interactive environment you are in the presence of a program "conteined on the Web page" which realizes this interactivity.
The hypermedia communication: An interactive way to communicate is defined by the communication via links which is created by programs, named browsers, whose aim is to display Web pages and in general all existing hypermedia. This way of communicating is so peculiar that it has been given a specific name (i. e., "hyper") and has been highlighted "outside" of the word media in the common language. However, it is always a way to communicate. A hypermedia or hyper multimedia object is a multimedia message and hyper. A multimedia message is a message that communicates with the multimedia technology. Hyper object is a message that contains references or links to other hyper objects. Once a hyper object is displayed with a browser, a link appears as an "exciting area" on the screen in the sense that, by pointing the area with the cursor, the mouse pointer turns into a pointing hand, and, by clicking on the area, another hyper object (or file in general) appears. Physically, a link is nothing but the address (= where is) plus the information on how to manipulate the object to which the link refers. In the case of web pages this information is contained in the URL of the object (= where the object is located on the Internet and how it should be manipulated).
Ultimately, a hypermedia or hyper-multimedia object is nothing but a formal language encoded message represented by a binary file, which, when interpreted by a program called browser, creates a communication using various types of communication techniques including the one mentioned above.