I've been using my augmented version of Lenny Librizzi's definition for a long time:
"Community garden- a shared green space which is planned, designed, built and
maintained by some community members for the use and enjoyment of the
entire community. Community gardens may be solely used to raise food for gardeners and/or the surrounding community, a decorative formal garden, an educational or rehabilitative facility, but as hard as the gardeners work to create the garden, the creation and nuturing of community remains a community garden's central mission."
Hope this helps.