What's the meaning of "No Obligation" in online home-based business opportunies?

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I see these all over the internet: Join now, it's free to join, no membership fee, no risk, and NO OBLIGATION! Since I am not that good in English because English is not my native language (I'm from the Philippines), I tried searching for the real meaning of this using the Internet, through search engines and online dictionaries and encyclopedia. The search results did not satisfy me. All I got are websites with words "no obligation" written in them! Can you help me please? To you, what's the meaning of "no obligation"?