Crypto has become the colloquial term and prefix for any technology using cryptography to aid any or all of its abilities.
Cryptography is the study and practice of how to send secure communications between two points while preventing any 3rd parties from intercepting and/or reading that information.
This requires encoding the information, so that only a specific key can be used to decode the message, rendering it gibberish to anyone without that key. The key might be a physical device or, in modern times, computer software that encrypts the information on one side and then decrypts it for the receiving party.
Digital Cryptography has become crucial for modern computer communication, ensuring not only greater privacy but also that the information has not been tampered with or changed in route.