every cryptocurrency that have been launched after bitcoin, and if you search some popular altcoins like litecoin you will found the same definition.
ok but these altcoins have diferent features and purposes like dash, monero and the most popular eth.
I think almost late reply here are repeating the answers. almost next to bitcoins are altcoin those are have more advantage in bitcoin security or speed for every transaction but they are late because bitcoin is the first succeed cryptocurrency online. also bitcoin is growing and more stores online are accepting bitcoin just like brazil that has many stores locally that can accept bitcoin as payment..