Privacy coins are the coins that let people to send and receive coins privately. Unlike Bitcoin and other crypto currencies whose transactions can be publically viewed on blockchain, privacy coin transactions do not appear on the public blockchain. Privacy coins use a technology that not only mask the sender and receiver address but also the transaction record.
The concept of making the sender, receiver and the transaction not just anonymous but also private was popularized by the privacy coins like Monero and Dash. Both of these privacy coins were created in 2014, Monero in April and Dash in January.
If the crypto currency transactions were already anonymous allowing the sender and receiver to hide their identity, why there was a need for coin to make every transaction private?