Marital coercion is a legal defense that can be used when someone is accused of committing a crime, but they were forced to do it by their spouse. It's kinda like saying "my husband/wife made me do it!"
For example, let's say a wife is charged with stealing a car. But she claims that her husband threatened to harm her if she didn't steal it. She could use the defense of marital coercion to say that her husband made her do it, and she had no choice.
Now, just because someone claims marital coercion doesn't automatically mean they will be free from punishment. The court will have to decide if the defendant's claims are true, and if they were under enough pressure from their spouse that they didn't have any other options.
But generally, if someone is found guilty of a crime and they can prove that they were coerced by their spouse, they may get a lighter punishment or even be acquitted of the charges entirely.