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Digital currency physical metal dogecoin coin on the gold bitcoins. Gold money concept.

Dogecoin is the hottest, quirkiest cryptocurrency on the planet.

The total value of the dogecoins in circulation is nearly $50 billion — not bad for a digital currency that started as a joke.

It is the No. 5 most-valuable cryptocurrency on the market, according to CoinMarketCap, having increased more than 6,000% this year.

The price of a dogecoin doubled again Friday after Tesla (TSLA) CEO Elon Musk tweeted about it for the umpteenth time (more on that in a bit). Demand for Dogecoin spiked so much this week, it briefly broke Robinhood's cryptocurrency trading system.

What is dogecoin?

Like all cryptocurrencies, dogecoin is a digital currency that can be bought and sold like an investment and spent like money.

Although each crypto is unique, it shares some similarities with its better-known peers — its code is based off the script for litecoin, for example. But it has a couple key differences.

Unlike bitcoin, which has set 21 million as the finite amount of the digital currency, dogecoin has 129 billion coins in circulatIon and will continue to make new blocks of coins available to mine each year. That's part of the reason one dogecoin is currently valued at about three dimes and a bitcoin is worth about $62,000.

Although cryptos are gaining more acceptance as a currency for purchasing goods, dogecoin doesn't have much mainstream real-world use. It has a few niche markets, including using dogecoin to tip online artists.