A quantum field theory (QFT) is a type of modern-physics theory that treats "everything" as fields, with particles considered to be fields, or depending upon how you look at it, particles are an emergent phenomena from the excitation of fields (i.e., a portion of a field above the ground state). A QFT can handle the physics problems that quantum mechanics addresses, and also has the advantage of modeling quantum-scale (atomic scale and smaller) mechanical phenomena that is taking place within a field such as an electric field or magnetic field. They also have the advantages of more ease in handling many particles and having a well-established, usable way of incorporating the effects of special relativity.
QFTs vary based upon a quantity called a coupling constant. Different coupling constants are valid for different circumstances, and a QFT is termed a strongly-coupled quantum field theory (or strongly-coupled QFT) or a weakly-coupled quantum field theory (or weakly-coupled QFT). The strong force has a strong coupling constant, a motivation for the terms.
Quantum electrodynamics (QED) is a particular (kind of) QFT addressing just one type of field: electric fields. QED problems are generally addressed using a perturbation theory, an approximation approach that is effective and useful for appropriate circumstances. Quantum chromodynamics (QCD) is a particular QFT that includes the strong force.