Sewadar is a Punjabi word for a volunteer who offers his/her services to a Gurdwara or to the Sikh community free of charge. It is a term used to refer to a person who performs sewa (work, service or assistance of any kind) without looking for any physical or spiritual reward or any payment of any kind. A sewadar helps purely because of his/her dedication to Guru/God and as part of his/her duty to the wider community. People of every religion are included in this service.
References
Sewadar Wikipedia(Text) CC BY-SA