The word trustee is a legal term that refers to a member of a trust, which can be set up for any of a variety of purposes, and is entrusted with the administration of property on behalf of others.
In the case of charities in the UK, a trustee is an unpaid volunteer who undertakes fiduciary responsibilites on behalf of the charity, subject to the provisions of the Charities Act 1993 (http://www.hmso.gov.uk/acts/acts1993/Ukpga_19930010_en_1.htm), which is regulated by the Charity Commission.
UK Legislation
Trustee Delegation Act 1999 (http://www.hmso.gov.uk/acts/acts1999/19990015.htm) specifically covers matters to do with land.
