What’s the meaning of all the world’s a stage?

“All the world’s a stage” is the opening line of a monologue in Shakespeare’s As You Like It:

All the world’s a stage,
And all the men and women merely players;
They have their exits and their entrances;
And one man in his time plays many parts,
His acts being seven ages …” (Act II, Scene vii)
The monologue is an extended metaphor in which life is compared to a play, with people playing different parts as they age. It is a commentary on both the ultimate brevity and meaninglessness of human life and the ways people may choose to reveal and conceal their identities.