Distributed vs parallel computing
This is partly a matter of terminology, and as such, only requires that you and the person you're talking to clarify it beforehand. However, there are different topics that are more strongly associated with parallelism, concurrency, or distributed systems.

Parallelism is generally concerned with accomplishing a particular computation as fast as possible, exploiting multiple processors. The scale of the processors may range from multiple arithmetical units inside a single processor, to multiple processors sharing memory, to distributing the computation on many computers. On the side of models of computation, parallelism is generally about using multiple simultaneous threads of computation internally, in order to compute a final result. Parallelism is also sometimes used for real-time reactive systems, which contain many processors that share a single master clock; such systems are fully deterministic.

Concurrency is the study of computations with multiple threads of computation. Concurrency tends to come from the architecture of the software rather than from the architecture of the hardware. Software may be written to use concurrency in order to exploit hardware parallelism, but often the need is inherent in the software's behavior, to react to different asynchronous events (e.g. a computation thread that works independently of a user interface thread, or a program that reacts to hardware interrupts by switching to an interrupt handler thread).

Distributed computing studies separate processors connected by communication links. Whereas parallel processing models often (but not always) assume shared memory, distributed systems rely fundamentally on message passing. Distributed systems are inherently concurrent. Like concurrency, distribution is often part of the goal, not solely part of the solution: if resources are in geographically distinct locations, the system is inherently distributed. Systems in which partial failures (of processor nodes or of communication links) are possible fall under this domain.