Is a process of converting plaintext into ciphertext to prevent unauthorized access?

The process of converting plaintext into ciphertext is called encryption.

Once encrypted, only trusted recipients (those who have a copy of the public encryption key) can revert the process and recover the plain text.

A related process is called authentication. It is used by the trusted recipient to ensure that the plain text was recovered correctly, since the wrong key will seemingly successfully decrypt the cypher into meaningless data.

Encryption and authentication are almost always used together.