A charity is an organisation established exclusively for charitable purposes (i.e. for the benefit of the public) and pursues its activities for public benefit not for private gain. Many community groups and voluntary organisations are charities.
Charity Law requires most charities (with some exceptions) to register with the Charity Commission.
By being registered, charities can gain benefits such as relief on business rates, tax relief and fundraising.
For general information about what a charity is and when they need to be registered with the Charity Commission see the PAVO information sheet 1.6 Charitable Status.