Quantum Field Theory (QFT) is the theoretical framework describing the quantization of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high energy physics as well as condensed matter physics and closely related to statistical field theory. Use this tag for many-body quantum-mechanical problems and the theory of particle-physics.
quantum-field-theory covers the theoretical description of many-body systems (such as fermionic gases in condensed matter) and high-energy physics/particle physics, starting from a given Lagrangian or Hamiltonian. You might hence also/only want to tag your question as condensed-matter or particle-physics, depending on your background. As QFT allows for a Lorentz-invariant formulation of quantum mechanics, general-relativity and special-relativity go well with quantum-field-theory.
The quantum field theories most worked on are special relativistic, and are sometimes known as relativistic quantum field theories, although it is more common to simply call it as [tag:quantum-field-theory] and use non-relativistic-quantum-field-theory for the non-relativistic QFTs. Examples of Relativistic QFTs include the following:
The latter, the Standard Model of Particle Physics, describes all experimentally known fundamental interactions (bosonic fields) and fermionic fields, except for gravity, which is classically described by general-relativity.
Many Quantum Field Theories, including the standard-model are worked out pertubatively.
Quantum field theory can also be formulated on a curved spacetime, corresponding to an external classical gravitational field.