This post is more in the way of information than it is a question. I was doing some background work for something and in the process found the source of the terms Event Horizon and Particle Horizon. They were coined by Wolfgang Rindler in the article Visual Horizons in World Models Mon. Not. Roy. Astr. Soc. vol 116, p. 662, 1956.

An event-horizon,[/i] for a given fundamental observer A, is a (hyper-) surface in space-time which divides all events into two non-empty classes: those that have been, are, or will be observable by A, and those that are forever outside As possible powers of observation.[/I]

A particle horizon,[/i] for any given fundamental observer A and cosmic instant t0 is a surface in the instantaneous 3-space t = t0 , which divides all fundamental particles into two non-empty classes: those that have already been observable by A at time t0 and those that have not.[/i]

It can be downloaded at Visual Horizons in World-Models | W. Rindler | digital library booksc