Marriage line is a short (usually around 1” long) horizontal line that lives under the pinky.
Some may have only one marriage line while many people have more than one.

You can learn more about your marital situation by observing the appearances of the marriage line, paying special attention to its shape, length, and depth. It indicates whether you will get married, when you will get married, and how satisfying your marriage will be.The number of marriage lines you have is not an indicator of how many times you will get married. If you have more than one marriage line, read your marriage based on the longest one.

Always read the marriage lines on both hands.
If there is a significant difference between the marriage lines of your two hands, your marriage or relationship are, or will be, filled with novelty.