Community Health is a term coined probably by someone in the year 2009 in the process of developing a strategy for the Wikimedia movement back then.
Another source is a journal article: "Decentralization in Wikipedia Governance" Andrea Forte, Vanessa Larco, and Amy Bruckman. (2009) Journal of Management Information Systems. 26(1) pp 49–72. To quote "We suggest that the Wikipedia community has remained healthy in large part due to the continued presence of “old-timers” who carry a set of social norms and organizational ideals with them into every WikiProject, committee, and local process in which they take part."
In 2009 the concern that sparked the creation of a community health taskforce was the decline in growth of Wikipedia.