When a guy says lets be semi casual (relationship wise) what does that entail?

6 months ago we were dating & we wanted it to grow into a relationship but It never happened. Now he wants to be semi casual with me but I don't know what that entails. Like is it a hook up? just flirty friends? or is it a relationship?!? Like what are some rules or boundaries of being semi casual with a guy?
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Now he's saying he wants to be casual. What does this mean?
When a guy says lets be semi casual (relationship wise) what does that entail?
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