Balance or impartiality, is sometimes used in reference to political content in the mass media

Mass media

Mass media refers collectively to all media technologies which are intended to reach a large audience via mass communication. Broadcast media transmit their information electronically and comprise of television, film and radio, movies, CDs, DVDs and some other gadgets like cameras or video consoles...

. This usage began in Britain in the early part of the 20th century when the Conservative Party

Conservative Party (UK)

The Conservative Party, formally the Conservative and Unionist Party, is a centre-right political party in the United Kingdom that adheres to the philosophies of conservatism and British unionism. It is the largest political party in the UK, and is currently the largest single party in the House...

 was unpopular and receiving little coverage through the BBC. In order to provide an intellectual rationalization for an increased level of Conservative content, Lord John Reith

John Reith, 1st Baron Reith

John Charles Walsham Reith, 1st Baron Reith, KT, GCVO, GBE, CB, TD, PC was a Scottish broadcasting executive who established the tradition of independent public service broadcasting in the United Kingdom...

, the BBC's founding General Manager and later Chairman, promoted a concept called balance.

In practise balance means ensuring that statements by those challenging the establishment are balanced with statements of those whom they are criticising, though not necessarily the other way round.