If someone is two-faced, it means they say nice things about someone to their face, but say bad things about them behind their back.
Matt is so two-faced. He told me I'm a great cook; then afterwards he told his other mates that my food is the worst he's ever eaten!
I really don't believe what Matilda says; I think she's a two-faced liar.
If someone loses face, they lose the respect of others.
Phillip lost face when no one came to his birthday party.
The masks in the image are used in mime, a kind of theatrical performance which uses no words. Instead, actors use facial expressions and movements of their hands and bodies to tell the story.