First developed in the mid-1970s, 'Asymmetric' or 'Public-Key' encryption overcame the Key Distribution Problem through the use of keys that could be shared freely (hence 'public key').
Each user has a 'Key Pair', two mathematically-related keys. Their 'public' key is widely shared with others who can use it to encrypt a message. The message can only be decrypted with the 'private' key (which is never shared).