What is Building Society?

Legal Definition
A building society is a financial institution owned by its members as a mutual organization. Building societies offer banking and related financial services, especially savings and mortgage lending. These institutions are found in the United Kingdom (UK) and several other countries.

The term "building society" first arose in the 18th century in Great Britain from cooperative savings groups. In the UK today, building societies actively compete with banks for most consumer banking services, especially mortgage lending and savings accounts.

Every building society in the UK is a member of the Building Societies Association. At the start of 2008, there were 59 building societies in the UK, with total assets exceeding £360 billion. The number of societies in the UK fell by four during 2008 due to a series of mergers brought about, to a large extent, by the consequences of the financial crisis of 2007-2010. With three further mergers in each of 2009 and 2010, and a demutualisation and a merger in 2011, there are now 44 building societies.
-- Wikipedia
Legal Definition
An association in which the subscriptions of the members form a capital stock or fund out of which advances may be made to members desiring them, on mortgage security.
-- Black's Law Dictionary