A “security” is defined VERY broadly, which would include an interest in a property or an interest in an LLC that would own the property. The key thing that makes is a security vs. a joint venture is that the investors are NOT involved in the management of the investment. So, if you are running the show and offering interests with a promise of a return, its a security. On the other hand, if you are a handful of people all invest together and everyone is a managing member, this is probably not a security.
Having said that, there are many exemptions from registration, which are too detailed to get into here, but if you are selling shares of your deal, suffice it to say that you will need to hire a lawyer to draft a private placement memorandum (aka “offering memorandum” or “PPM”) and file exemption forms with the SEC and every state in which you solicit investors. You can expect to pay 10 - 25k for the PPM, which you’ll fork out up front, but ask the investors to reimburse you for.
The problem with it being security is solicitation. You can only solicit friends, family, and people you have an existing business relationship with. If you solicit to the general public, even in a small way, EVERYONE that invests from that solicitation must be an “Accredited Investor” (rich, experienced, and sophisticated people that meet the SEC guidelines).
This is just an overview, there are many intricacies involved that require getting qualified legal counsel.