At first indulgences were limited to 40 days, and were remissions of punishment and of sin and a specified quantity of penance. Purgatory came to be thought of as the place where penance was performed after life; a place in time, rather than eternal like heaven. Thus an indulgence would limit the time the sinner spent in purgatory. Pilgrimage might be undertaken as expiation of particularly serious sins. When preaching the First Crusade, Pope Urban II granted a *plenary indulgence, saying all those who went might count that journey in lieu of all penance. It may be that the very first text printed using movable type was an indulgence issued by Pope Nicholas V in 1454. [< Lat. indulgentia = leniency, concession.]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.