There are over 3000 languages spoken by the human race today. The language you decide to communicate your thoughts and product details in must be of a standard that enables the viewer to understand what you are trying to say. Languages are not restricted to verbal processes but can also be based on visual communication eg. sign languages and the written word. Codes and other kinds of communication systems are also languages eg. Morse code. A language in this sense is a system of signs for encoding and decoding information. HTML, or HyperText Markup Language, provides a means of formatting content in ways that browsers, such as Internet Explorer and Firefox can understand - they then act as a decoder or translator, converting the code into a visual and text format that humans (hopefully) can understand.
What role Meta tags do play in Search engine optimization (SEO)? I think this question can be partly answered by stating - The effectiveness of tags depends on the ever changing processes and criteria search engines use to rank pages.