String theory is not a quantum field theory in the traditional sense. While it does have quantum mechanical properties, it is a more general framework that goes beyond conventional quantum field theories. In string theory, the fundamental objects are not point-like particles, as in quantum field theories, but rather one-dimensional extended objects called strings. These strings can vibrate and interact with one another.
String theory incorporates quantum mechanics and includes gravity as well. It attempts to provide a unified description of all fundamental forces and particles in nature, including gravity, electromagnetism, and the strong and weak nuclear forces. By doing so, it aims to reconcile general relativity (which describes gravity on a large scale) with quantum mechanics (which governs the behavior of particles on a small scale).
While quantum field theories are used to describe the behavior of elementary particles and their interactions, string theory provides a more fundamental framework that encompasses quantum field theories as special cases in certain limits. However, it is important to note that string theory is still a subject of active research and has not yet been experimentally confirmed.