May 5 (Reuters) - Facebook Inc's oversight board on Wednesday upheld the company's decision to ban former U.S. President Donald Trump from the service, but called on the company to decide within six months whether to permanently ban him or restore his account.

Here are some key facts about how the board works:

WHAT DOES THE OVERSIGHT BOARD REVIEW?

The board, which some have dubbed Facebook Inc's "Supreme Court," can overturn the company's decisions on whether some individual pieces of content should be displayed on Facebook or its photo-sharing platform Instagram. It can also recommend changes to Facebook's content policy, based on a case decision or at the company's request, but these are not binding.

The board, which only makes rulings on a small slice of Facebook's content decisions, has said it aims to pick cases with wider relevance. It said it has received more than 300,000 cases since it opened its doors in October 2020.

Cases so far have involved issues such as hate speech, violence and nudity. Facebook has said the board's remit will in future include ads, groups, pages, profiles and events, but has not given a time frame.

It does not deal with Instagram direct messages, Facebook's messaging platforms WhatsApp and Messenger, its dating service, or its Oculus virtual reality products.

HOW DOES THE BOARD WORK?

The board, which is supported by a staff, decides which cases it reviews. Cases can be referred either by a user who have exhausted Facebook's appeals process or by Facebook itself for "significant and difficult" cases.

Each case is reviewed by a five-member panel, with at least one from the same geographic region as the case originated. The panel can ask for subject-matter experts to help it make its decision, which then must be finalized by the whole board by majority vote.

The board's case decision - which is binding unless it could violate the law - must typically be made and implemented within 90 days, though Facebook can ask for a 30-day expedited review for exceptional cases, including those with "urgent real-world consequences."

Users will be notified of the board's ruling on their case and the board will publicly publish the decision. When the board gives policy recommendations, Facebook has to publish a response within 30 days.

WHO IS ON THE OVERSIGHT BOARD?

The board currently consists of 20 people but will eventually have about 40 members.

Facebook chose the four co-chairs - former federal judge Michael McConnell and constitutional law expert Jamal Greene from the United States, Colombian attorney Catalina Botero-Marino and former Danish Prime Minister Helle Thorning-Schmidt - who selected 16 other members jointly with Facebook.

Some picks resulted from the global consultations conducted by Facebook to obtain feedback on the oversight board.

The members, who are part-time, also include civil rights advocates, academics, journalists, a Nobel Peace Prize laureate and a former judge of the European Court of Human Rights.

The members are paid by a trust that Facebook has created and will serve three-year terms for a maximum of nine years.

The trustees can remove a member before the end of their term for violating the board's code of conduct, but not for content decisions. (Reporting by Elizabeth Culliford; editing by Kenneth Li, Jonathan Oatis and Nick Zieminski)