Bitcoin is the first decentralized cryptocurrency ever invented by Satoshi Nakamoto, whose identity is not known, and released in 2009. Because Bitcoin was the first cryptocurrency to exist, all digital cryptocurrencies created since then are called Altcoins. Dash, Ethereum, Ripple and hundreds of other coins are Altcoins because they are not Bitcoin.
Bitcoin is completely digital, designed to be ‘self-contained’ for its value, with no need for banks or other middlemen to move or store the money. Bitcoin transactions are irreversible.
Once you own Bitcoin, it behaves like physical gold: it possesses value and trades just as if it was nuggets of gold in your pocket. You can use your Bitcoins to purchase goods and services on and offline, or you can tuck them away and hope that their value increases over the years.