What do in-network and out- network mean in regards to choosing health insurance?

I am choosing a health insurance to benefit myself, but i am not sure what in-network and out-network means so therefore i cannot make my decision. Does anyone know what these two mean? Anything you know helps!
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In-Network means choosing one of the plan's providers that has agreed to a pre-set formula for reimbursement. You usually pay a lower deductible for using In-Network providers. Out-Network means the provider has not agreed to the reimbursement formula of the insurance plan. You will often pay a higher deductible, but you get to choose any doctor you like.
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