Simplify the following text for a Grade 4 native English-speaking person.
Original: These are common crossword variants that vary more from a regular crossword than just an unusual grid shape or unusual clues ; these crossword variants may be based on different solving principles and require a different solving skill set .
Simplified: A crossword , or crossword puzzle , is a popular type of word puzzle . A crossword is made up of black and white squares ( called a ` grid ' ) and a list of clues .