As senders, we encode messages, and our recievers decode them. The codes we use are systems of signs. The sign itself is called the signifier, and the object, idea or feeling it represents is called the signified. In interpersonal communication, signs are either verbal, or non verbal.
Most of the verbal signs we use are symbolic. In other words, there is no logical reason why that particular sound should signify that particular idea. Over time, the group of people or culture using a particular language broadly agrees on this correlation between signifier and signified. It is a conventional and abitary relationship.