Satoshis are the smallest unit of the Bitcoin cryptocurrency. One satoshi is equal to 0.00000001 BTC (i.e., one hundred millionth of a Bitcoin). This unit is named after the creator of Bitcoin, Satoshi Nakamoto.
Satoshis, also known as 'sats', are used to represent the amount of Bitcoin in a transaction. For example, if a transaction sends 0.00000021 BTC, it sends 21 sats. The use of sats allows for more precise representation of Bitcoin amounts, as the BTC unit can be divided into a much larger number of sats.
Sats are commonly used to represent small amounts of Bitcoin, such as fees or microtransactions. They are also used to represent the balance of a Bitcoin wallet, and to specify the amount of Bitcoin to be sent in a transaction.
Sats are to a bitcoin what cents are to a dollar. It's the same thing, it's just that bitcoin is one whole coin and sats are the fractions of a coin. There are 100,000,000 satoshis (sats) in one bitcoin.
And, yes, it's real money.