What is a private key?

By analogy with the password or a confidential code by means of which it is possible to get access to a certain system the private key (private key, secret key) is a method of access to execution of operations with use of the addresses associated with it providing confidence that nobody, except the owner of a private key, will be able to get such access.

The private key represents the unique string generated in a random way, and in some software can be presented for convenience in the form of a mnemonic key (seed) phrase which is transformed to a private key.

The private key is confidential information. It shall be stored in the safe place and shall not be published in open access in any kind.