Key points:
- Bitcoin is a digital currency that people can buy and sell online.
- It has gone up more than 3% in the last 24 hours, which means it is worth more now than before.
- The total amount of bitcoins is limited to 21 million, but not all of them are available yet.
- Bitcoin is very popular and valuable, so it has a high market cap ranking.

Summary:
Bitcoin is a kind of money that you can use on the internet. It has gotten more expensive in the past day, because people want it more. There are only 21 million bitcoins in the world, but not all of them are out yet. Bitcoin is very important and valuable, so it is number one among other kinds of money. Read from source...

1. The headline is misleading and sensationalized. It implies that Bitcoin has increased by more than 3% in the last 24 hours, which is not a significant or impressive gain for such a volatile asset. A better headline would be something like "Bitcoin Fluctuates Within 3% Range Over Past Day".