What is an event related potential?

An event related potential, as the name suggests, represents changes in electric potential in response to an event, for example a light flashes to the test subject as part of an experiment, which are caused by a neural site in the brain.

More formally, an event related potential, or ERP, is defined in (Luck, 2014) as follows. “An ERP component can be operationally defined as a set of voltage changes that are consistent with a single neural generator site and that systematically vary in amplitude across conditions, time, individuals, and so forth. That is, an ERP component is a source of systematic and reliable variability in an ERP data set.”

This means that if an ERP component exists, it can be consistently seen occur in other experiments, with slight changes depending on the conditions, time, individual etc, caused by the same neuroanatomical site.