Bancha (番茶), is lower grade tea as compared to Sencha. The cultivating and processing method is same as Sencha, but it's produced from older tea leaves, therefore lower grade. The older tea leaves are those at the bottom side of the tea tree. The other way to produce Bancha is to harvest the tea leaves at later time (second flush, third flush).
Bancha has lower caffeine content because older tea leaves has lower caffeine.