What is on the Back of a Penny?

By GovMint :

The back, or reverse, of the current circulating Penny features the Union Shield design that was introduced in 2010. This design depicts a shield with 13 vertical stripes and a horizontal bar that symbolizes the original 13 states joined together in a single union. The shield is topped with the national motto "E Pluribus Unum," which means "Out of many, one."

Before the Union Shield design, the penny's reverse underwent several changes. From 1959 to 2008, the reverse showed the Lincoln Memorial design that commemorated the 150th anniversary of Abraham Lincoln's birth. Prior to that, from 1909 to 1958, the reverse featured two wheat stalks in a design known as the Wheat Penny design.

Sources Used:

https://www.usmint.gov/coins/coin-medal-programs/circulating-coins/penny