Generally, string is a thin piece of fiber which is used to tie, bind, or hang other objects. String can be made from a variety of fibres. You can get different kinds, twine for example. The term has more specific meanings, within certain academic disciplines.
In biology, a string is a chain of biochemicals.
In various branches of mathematics and computer science, strings are sequences of various simple objects (symbols, tokens, characters, etc.), used in many contexts. See Character string (computer science).
A string is a vibrating cord of metal, nylon, gut or other substance such as wound hair that vibrates to produce a tone in a variety of musical instruments. Strings can also refer to the section of an orchestra or band consisting in stringed instruments. See string instrument.
In theoretical physics, a string is the basic object of study in string theory. In string theory, strings replace the notion of elementary particles in quantum field theory. See also: open string, closed string.