I wouldn’t call it a “mask”, because it implies deception. Depending on who you are around, you show (and hide) different treats of your personality: In an employment setting you do not act the same way you would act when you hang with your boys (or girls, respectively) - you show different aspects of your personality while you are with your significant other, rather than with your parents. Also, your online behavior would be different from your offline behavior when navigating public situations.

Different people around you and/or different social settings make you filter things regarding your personal beliefs and/or personal traits.