Depending on exact paradigm, iterations are also called round or frame
ERP context: Uninterrupted period of short experimental activity relative to a single (not repeated) sequence of subtrials. Typical duration: 0ms to 30s. Example for a frame: Period needed to record ERP signals during the single highlighting sequence of all elements (rows and colums, or all symbols on the screen) of a speller matrix. Typical setups would comprise several frames of stimuli in order to collect increasing evidence about the target. Example for a round: Period needed to record ERP signals during the unrepeated sonification of every single tone/direction in a spatial auditory experiment.