Literacy has been described as the ability to read for knowledge and write coherently and think critically about the written word. Literacy can also include the ability to understand all forms of communication, be it body language, pictures, video or sound (reading, speaking, listening and viewing). Evolving definitions of literacy often include all the symbol systems relevant to a particular community. Literacy encompasses a complex set of abilities to understand and use the dominant symbol systems of a culture for personal and community development. In a technological society, the concept of literacy is expanding to include the media and electronic text, in addition to alphabetic and number systems. These abilities vary in different social and cultural contexts according to need and demand.