What it means has been defined by Congress:
49 USC 44809
(h) Community-based Organization Defined.--In this section, the
term community-based organization' means a membership-based
association entity that--
(1) is described in section 501(c)(3) of the Internal
Revenue Code of 1986;
(2) is exempt from tax under section 501(a) of the
Internal Revenue Code of 1986;
(3) the mission of which is demonstrably the furtherance
of model aviation;
(4) provides a comprehensive set of safety guidelines for
all aspects of model aviation addressing the assembly and
operation of model aircraft and that emphasize safe
aeromodelling operations within the national airspace system
and the protection and safety of individuals and property on
the ground, and may provide a comprehensive set of safety rules
and programming for the operation of unmanned aircraft that
have the advanced flight capabilities enabling active,
sustained, and controlled navigation of the aircraft beyond
visual line of sight of the operator;
(5) provides programming and support for any local
charter organizations, affiliates, or clubs; and
(6) provides assistance and support in the development
and operation of locally designated model aircraft flying
sites.
(i) Recognition of Community-based Organizations.--In
collaboration with aeromodelling stakeholders, the Administrator shall
publish an advisory circular within 180 days of the date of enactment
of this section that identifies the criteria and process required for
recognition of community-based organizations.''.
So which organizations meet those criteria has not been fully defined, although the recent FAA circular 91-57B expands somewhat on that:
7.1.2 The Aircraft is Operated in Accordance With or Within the Programming of a CBO’s Set of Safety Guidelines That are Developed in Coordination With the FAA. Once the FAA has developed the criteria for recognition of CBOs and started officially recognizing CBOs, those CBOs’ safety guidelines will be available for use. During this interim period, the FAA offers two means to satisfy this statutory condition. Recreational flyers should be able to explain to an FAA inspector or law enforcement official which safety guidelines they are following.
7.1.2.1 The FAA acknowledges that existing aeromodelling organizations have developed safety guidelines that are helpful to recreational flyers. An example is the AMA safety guidelines, which have previously been reviewed by the FAA as part of the organization’s Recognized Industry Organization (RIO) status for participation in the National Aviation Events Program (refer to FAA Order 8900.1, Volume 5, Chapter 9, Section 6, Issue/Renew/Reevaluate/Rescind an Air Boss Letter of Authorization). These or existing safety guidelines of another aeromodelling organization may be used for recreational operations, provided the guidelines do not conflict with the other statutory conditions of 49 U.S.C. § 44809(a).