A cross is an ancient execution device on which people were said to be crucified. The Romans had several instruments that were called crosses. When a person underwent crucifixion, they died of suffocation. One of the more common types of cross had a single vertical stake with a cross member near or at the top by which a person is either nailed and/or tied with outstretched arms.
Orthodox Christianity holds that Jesus was nailed to a cross--not a stake since in John 20:25, Thomas stated that he would not believe that Jesus had risen from the dead unless he saw "...in His hands the imprint of the nails..." A cross would require at least two nails, one for each outstretched hand.