An overdraft is a source of short term capital. An overdraft allows you to withdraw more money from your bank account than you have available in your account balance. The bank essentially lends you the difference, and you can use the extra funds for a short period of time, usually until your next deposit. This is a convenient way to get access to quick cash when you need it, but it typically comes with high interest rates and fees, so it's important to use it wisely and pay it back as soon as possible.