A retail bank branch, where people can perform money-related tasks. Also a common location to find an ATM.
This emoji came to also mean "slacking off" or evading responsibility in Japan, due to the BK letters being associated with the slang term bakkureru.
Bank was approved as part of Unicode 6.0 in 2010 and added to Emoji 1.0 in 2015.
U+1F3E6
? Bank