The Lightning Network is the payment system which allows us to transact with other people or businesses around the world using Bitcoin - the world’s first and leading cryptocurrency.
With the Lightning Network, you can send payments peer-to-peer almost instantaneously with little to no fees. It also makes money completely programmable, making it possible to split payments from one sender to multiple recipients or automate payments at regular intervals. All of this would not be possible with traditional payment rails.
As the Lighting Network tends to be used for smaller amounts, payments are denominated in "satoshis" (or "sats" for short). Sats are named after the pseudonymous creator of Bitcoin, Satoshi Nakamoto. You can think of sats as the bitcoin cents. There are 100 million sats in one bitcoin. The value of bitcoin changes daily, but $1 is equivalent to roughly 4000 sats. You can check the current price of bitcoin here.