What does the "c" in "E=mc²" represent?

More Questions:

What term was coined in 1983 to market the "Gavilan SC" portable computer?

A statue of Billy Bremner stands outside the ground of which football stadium?

What gift is first presented on the fifth day in the song "The Twelve Days of Christmas"?

What is the common name for "graphospasm"?

Who played Mallory Keaton on the TV show "Family Ties"?

What French word for "jewel" became a common name for American movie houses?

What are the escape tunnels in the film "The Great Escape" called?

What Monty Python movie was banned in Norway?

What former "American Idol" hopeful sported a hairstyle that inspired the term "ponyhawk"?

What TV show featured Ellen DeGeneres as a receptionist?

What 1972 comedy begins with "Once upon a time there was a plaid overnight bag"?

What Ukrainian city hosted the last World War II summit of the "Big Three"?

Which of Shakespeare's plays involves a pound of flesh?

Which Bond actor passed away on May 23, 2017?

Which charcter did Neil Hamilton play in the original TV series "Batman"?