The private key is an unencrypted private key. Anyone with access to your private key can control your wallet. If you do not have your private key, you do not own your wallet. The private key is essentially a true random number. Stored as a byte array in a computer. Here take an example of the BTC and ETH private keys:
BTC：L2XgPM8M7i2TT9BqEBtaYLcSwXHC7oScYN2GTLFDDyKwiWXAAMwi
ETH：7bf7d40446c09a9c1e5a9019650d9c398680fb2d323824cc85ba88026b057843
In Ethereum and Bitcoin, the private key has two main roles:
- The private key generates the public key, thus deriving the transaction address
- The private key lets you authorise transactions
For EOS, the role of private key is a little different. It is used to generate transaction signatures, not to generate transaction addresses.
Because EOS introduces the concept of an account, the EOS account is similar to the ENS domain, so the EOS transaction address is not derived from the private key.
Here take an example of the EOS private key:
EOS: 5KcryqKESci1TJbW4bsSVRStdcPRdqmJets1f9G225iqW3KBfEC