A restrained and self-effacing manner.
Restrained laughter; a restrained foreign policy.
He greeted her for the first time in three years with a restrained embrace.
When you don't show your emotions, this is an example of when you might be described as restrained.
When you have a tasteful, simple black dress with no ornamentation, this is an example of an outfit that would be described as restrained.
When you are tied up in handcuffs and you cannot freely move your arms, this is an example of when you are restrained.
When you have your seat belt on in the car, this is an example of a time you are restrained.