I ask this question as the two seem to be very closely related and are sometimes taken to be one and the same (in the notion of microcausality in QFT), which has left me confused as to what meaning of the two concepts.
My understanding of locality (which, if incorrect, please let me know) is that particles can only directly interact with one another if they are in contact with one another (implying that the interaction occurs at a single point), i.e. no action-at-a-distance (particles at distinct points cannot exert a direct influence on one another).
Thus, in the case of QFT, the value of a Lagrangian density at a given point should only depend on the values of the fields at that point, along with a finite number of their derivatives (to explain interactions with fields infinitesimally close to that particular point). In summary, the dynamical state of a QFT at a given point in spacetime should be locally determined (i.e. the dynamics of a physical system should only depend on the local behaviour of the fields, and not on their global behaviour)
As far as I understand it, causality is the statement that two physical systems cannot "communicate" if they are separated by a space-like interval.
In QFT there is the concept of microcausality, in which fields must commute with one another if they are separated by a space-like interval. However, it is often formulated by saying that two fields measured simultaneously must commute unless they are located at the same spatial point. To me this seems almost the same statement as given by locality?!