Wiktionary
n. (context UK English) An organisation which represents an entire sector of industry or the community to the government, often incorporate other organisations in that area.
Wikipedia
A peak organisation or peak body is an Australian term for an advocacy group or trade association, an association of industries or groups with allied interests. They are generally established for the purposes of developing standards and processes, or to act on behalf of all members when lobbying government or promoting the interests of the members.
While there is no official granting of Peak Body status, peak bodies are widely accepted as the legitimate "voice" or representative of a profession or industry, as opposed to just a geographic/commercial/cultural/political subset of that profession, as evidenced by requests for media comment and inclusion in government consultations. They often have to present codes of conduct or ethics which can be used in legal cases determining negligence, can conduct industry-focused lobbying, and also can be providers of mandatory industry training.
In the commercial sector they allow competing companies to meet to discuss common issues without the risk of breaching the Competition and Consumer Act 2010 which outlaws collusion between competitors which would affect the operation of a free market.