Simplify the following text for a Grade 10 native English-speaking person.
Original: The World Series of Poker ( WSOP ) is a world-renowned series of poker tournaments held annually in Las Vegas and , since 2005 , sponsored by Harrah 's Entertainment .
Simplified: WSOP or the World Series of Poker is one among the biggest poker tournaments in the gambling world , which has been organized officially , in 1970 .