Bitcoin is a type of digital currency. It is also a payment system and fast approaching unit of account status. Bitcoin was created in 2009 by someone named Satoshi Nakamoto. To this date, no one knows who Satoshi is. There are many theories (Elon Musk, a supercomputer in China, etc.), but no one has officially stepped forward to claim the honor. As part of the creation, s/he also created the first blockchain database. Here's a link to the white paper (Bitcoin: A Peer-to-Peer Electronic Cash System) which explains how bitcoin works.
What problem did Satoshi solve in the white paper? S/He made it possible for a technology to be the intermediary by coming up with a logic to obtain consensus by all parties. In this way, no "trust" broker like a bank or lawyer is needed.
The number of Bitcoin available in the market is limited to approximately 21 million. There are approximately 16.7 million bitcoin on the market today (you can see how many bitcoin are currently on the market by clicking here). As of 11/26/2017, bitcoin is worth a little over $9,000. You can check on the latest bitcoin price here.
Due to its popularity, you can use Bitcoin at numerous stores. Some of these stores include: WordPress.com, Overstock.com, Subway, Microsoft, Reddit,Virgin Galactic, OkCupid, Namecheap, CheapAir.com, Expedia.com, Gyft, Newegg.com, and Whole Foods.
In addition to being able to send an unlimited amount of money to anyone with a cell phone, Bitcoin transactions are also anonymous. As President Obama stated, if the govt. can’t crack encryption, then people are walking around "with a Swiss bank account in their pocket."