Webster defines Volunteerism as

Pronunciation: \ˌvä-lən-ˈtir-ˌi-zəm\
Function: noun
Date: 1844
1 : voluntarism
2 : the act or practice of doing volunteer work in community

–noun
1. voluntarism (def. 2).
2. the policy or practice of volunteering one's time or talents for charitable, educational, or other worthwhile activities, esp. in one's community.