A "symbol" here is something symbolic and used for communication. A language is a collection of words, but semiotics thinks of it as a collection of symbols. If you think about it this way, you will be able to handle it with means other than words, specifically with electrical signals.
Signs and marks are also types of symbols.
The fields of philosophy , linguistics, and logic have been around for a long time, but this site summarizes them as semiotics. The way we relate to symbols is different.