To dream that you are wearing a costume, signifies that you are putting on a facade toward others. Your true self is not being revealed and you are not being completely honest with people around you.
A role you play, want to play, or want others to think you play.
The
Impression you want to give to others, or the kind of self-image you
Want to have
A disguise, a wish to be disguised, or a desire to not be recognized or seen
A context, role, or situation you're exploring, such as your role in a potential new job or in a different type of relationship than you're used to