‘Users’ is the generic term for those for whom you provide a service. For example, if you run a scrap store and provide materials for local play groups then the play groups are your users (and the children and Mums/Dads/Carers are the playgroup users and could be considered your ‘end’ user i.e. the last user in the chain). User is generally synonymous with client, service user, customer, and passenger and so on.
In the last 40 years there has been a shift away from philanthropy (in which a better off group provide a service to those less well off) to a self-help ethic in which those who need a service have come together to provide it themselves on their own terms. This democratisation of the voluntary groups has had a profound impact as in many cases now the users may also be the members and may be on the committee as well. A common source of tension on committees is caused by having individuals present from both of the aforementioned perspectives (philanthropy v self-help).
If you provide a service (i.e. change batteries in hearing aids) then the users are those who use (or receive) the service. However, in many cases users and members are one and the same. In either case it makes sense to give them the chance to be on the committee even though it will raise the issue of conflict of interest.