Wiktionary
long hundred
n. (context historical English) One hundred and twenty (120), 12 x 10.
WordNet
long hundred
n. the cardinal number that is the product of ten and twelve [syn: great hundred, 120]
Wikipedia
Long hundred
The long hundred, great hundred, or twelfty is the "hundred" of six score ( 120) used in Germanic languages prior to the 15th century. The number was simply described as hundred and translated into Latin in Germanic-speaking countries as ( Roman numeral c.), but the qualifier "long" is now added because present English uses the word "hundred" almost exclusively to refer to the number of five score ( 100) instead.
The long hundred was 120 but the long thousand was reckoned decimally as 10 hundreds ( 1200).