Communication is usually defined as the transmission of information. The term can also refer to the message itself, or the field of inquiry studying these transmissions, also known as communication studies. The precise definition of communication is disputed. Controversial issues are whether unintentional or failed transmissions are included and whether communication does not just transmit meaning but also creates it. Models of communication aim to provide a simplified overview of its main components and their interaction. Many models include the idea that a source uses a coding system to express information in the form of a message. The source uses a channel to send the message to a receiver who has to decode it in order to understand its meaning. Channels are usually discussed in terms of the senses used to perceive the message, like hearing, sight, smell, touch, and taste.