What is the ruling on a girl going out publicly with her fiancé without a marriage contract, and is this considered seclusion (khalwa)?

Forbidden seclusion (khalwa) is when a man is alone with a woman who is not a mahram to him, in a situation where they are safe from being seen by others. Going out with one's fiancée to public places is not seclusion, but it is forbidden because she is a non-mahram to him.