There was a time, when portable music players were referred to as MP3 players; mp3 because that’s the file type that was stored, and player because that's all that the device did/could. Then, when Apple entered - and eventually dominated - the industry, all mp3 players where colloquially referred to as iPods. A similar story can be told about the new digital currencies, known by many simply as bitcoin. Bit because its driven by bits and coin because it’s a new monetary system.
Bitcoin is simply one of many new technologies known together as digital currencies. They are all trying in different ways to pioneer a system of exchanging and storing value. Bitcoin was not the first such currency but it is the largest by a substantial margin. It is also the oldest digital currency that is still in circulation and it is the one that is most widely accepted by retailers. Born out of the ashes of the 2008-financial crisis, the digital currencies are all driven by the same agenda: to make large banks and other transactional intermediaries obsolete. This drives the main objective of all the new coins: to make transferring of money a simple act that can be performed with the same truism as sending an email.
The remaining objectives vary by coin technology. Some of the alternative coins, as they are known, focus their efforts on security and anonymity. Prominent examples are the ZCASH, MONERO and PIVX coins. Other technologies are more focused on transactional speed and flexibility. Examples are DASH, Litecoin and Ripple. There are many more coins than these and we haven't even touched on Ether/Ethereum. Ether is the second largest crypto coin by market capitalization and it certainly deserves a post of its own.