A Private Key1) is a Cryptographic Key used with a Public Key Cryptographic Algorithm that is uniquely associated with an entity and is not made public. In an asymmetric-key ( Public Key) cryptosystem, the private key has a corresponding Public Key. Depending on the algorithm, the private key may be used, for example:
A Private Key, also known as a secret key, is a variable in cryptography that is used with an algorithm to encrypt and decrypt code. Secret keys are only shared with the key’s generator, making it highly secure. Private Keys play an important role in symmetric cryptography, asymmetric cryptography, and cryptocurrencies.
The complexity and length of the private key determine how feasible it is for an interloper to carry out a brute force attack and try out different keys until the right one is found.
Public Key are for encrypting data by anyone with access to the Public Key. The Private Key is required to decrypt the data, which is why the Private key needs to be kept secret.
Source: https://searchsecurity.techtarget.com/definition/private-key