volunteer

1. A person that that actively takes on a task, responsibility, or project on his or her own accord without needing to be assigned, ordered, or told to do so. Often a volunteer is not paid for the work that they provide. For example, a volunteer may desire to work at a company's charitable events with or without pay and may even request to do so without being asked or told to.

2. Act of taking the initiative on a task, responsibility or project. This could be as a response to a request or by making the initiative to do so. For example, a group can volunteer to research an issue as a response to a request.