An ERP is an event-related potential. Really, it is a time-locked EEG record of activity related to a stimulus presentation or some cognitive event. ERPs are used by cognitive psychologist
s to determine what's going on in the brain during specific mental processing.
To record ERPs, EEG is recorded from the brain of a participant concurrently with the presentation of a stimulus. The records are averaged together, in the hopes that random electrical activity will average out, leaving only the activity related to the processing of the presented stimuli.