A more thorough explanation:

Definition: Occult marriage is a type of confidential marriage where only the two parties and the officiant are present at the ceremony. It is also known as a confidential marriage. Occult marriages are neither witnessed nor recorded in public records, but are recorded in nonpublic records. Although rarely performed, they are generally legal. To obtain an occult marriage, the parties must each be at least 18, must be of the opposite sex, and usually must have lived together for an extended period. In ecclesiastical law, such a marriage is termed an occult marriage or, if performed in the strictest secrecy, a marriage of conscience.

Example: In California, couples can opt for an occult marriage if they want to keep their marriage confidential. This allows them to go through all the formalities but have the records of the marriage, including the license, remain confidential. However, it does not relate back to the time when the parties started holding themselves out as a married couple and thus it can have consequences in determining the extent of marital or community property or various other rights.