A Bank is a facility that allows any player (except Ultimate ironmen) to deposit and withdraw their items safely. You can identify a bank by looking for a hanging sign with a Gold bar on it. You'll need to right click the npc with a grey suit inside to access your bank Currently, there is no limit to how many items you may store into the bank. Sometimes you'll come upon an npc that looks just like the banker in various spots around the map that will deposit any item you have on you for your convenience. If you happen to die with any untradeable items or capes, they will be automatically deposited into your bank.
Trivia[]
You will find bankers in construction sites where there should be an actual bank until the building is built in a future update.