Clad is considered ----USA coins made in 1965 up to now. Sometimes known as sandwich coins also because of the way the edges of the dimes, quarters and half dollars look.
Along with what dimeman said...US coinage...besides nickles....were silver up till 1964. After that they "Cladded" diferent metals together, silver, copper, nickle and zinc together to cut the cost of of the coinage...looks like a sandwich from the side. Hope this helps. Kieth