Things that require belief to exist

Things that only exist if enough people believe in them. They can be created by speaking.

particular languages
money
debt
physical property
intellectual property
laws
marriage
contracts

governments

nations
schools
churches
companies
sports
games
authority
prestige
fame
personal names
self-fulfilling prophecies
the sacredness of a flag
war
peace

If this interests you, you might enjoy reading about the following terms
"socially constructed"
"consensus reality"