Bitcoin is the original cryptocurrency, created in 2009. It is based on a decentralized peer-to-peer network, and its own currency, Bitcoin, is mined through a process known as proof-of-work.
Bitcoin is the largest and most well-known cryptocurrency, with a market capitalization of over $100 billion.
Altcoins are all the other cryptocurrencies that exist besides Bitcoin. These include popular coins such as Ethereum, Litecoin, and Monero. There are literally thousands of altcoins, with new ones being created all the time.
Most altcoins are based on the same basic principles as Bitcoin, but there are some notable exceptions. Ethereum, for example, uses a different consensus algorithm known as proof-of-stake.
The main difference between Bitcoin and altcoins is that Bitcoin is far more widely adopted and accepted than any other cryptocurrency. This gives it a much higher level of liquidity and stability.
Altcoins are much more volatile and tend to be much less liquid. Another key difference is that Bitcoin is designed to function as a global currency, while most altcoins are only meant to be used on specific platforms or within specific communities.