Could anybody please explain to me what this expression (the floor is yours) means? and on what occassion do we use it? thanks
You're the speaker now, You may speak now
the senate, the house of representatives, any formal meetings where a presenter stands before attendees, maybe. It's usually said when you're done making your point or your time is up to mean the 'floor' is available for the next speaker/presenter. It's always used when you hear words like bill, motion, etc. So, you wouldn't yield the floor in a staff meeting. You might yield the table. Just kidding Emotion: smile
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 Marius Hancu's reply was promoted to an answer.

You may start your presentation now. You can start now.

as far as I know, the expression explains that he or she is telling you that if you are in a presentation or something, its like the stage is yours so u can say what u want.

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The floor is yours means, the stage is yours and you can start your speech.