A collection of several thousand hidden websites that are \"online\", where someone can buy drugs, guns, stolen identities, social security numbers, hacked website credentials, and all matters of other illegal items using cryptocurrencies like bitcoin (BTC). Silk Road is the most famous Dark Web online marketplace that gained notoriety after being shut down by the FBI in 2013.
Example
“Silk Road, one of the most notorious dark web marketplaces, processed over $1 billion in Bitcoin transactions before the FBI shut it down in 2013.”