Picture a long train with lots of carriages that look exactly the same. Each carriage is a "repeating unit" and the entire train represents a polymer. In chemistry, a repeating unit is a group of atoms that appears over and over again along a polymer chain.

Polymers are like super long chains made up of the same small block, repeated hundreds or even thousands of times! That small block is the repeating unit. When drawing the structure of a polymer, we show the repeating unit inside large brackets with bonds sticking out on both sides. This indicates that the polymer chain extends on either side of the unit.

We also add a subscript 'n' after the closing bracket. This 'n' represents the number of repeating units in the polymer. A typical polymer has a lot of repeating units, so think of 'n' as a super large number.

A polymer's repeating unit comes from the monomer used to make it. Some polymer names are just the monomer name with the prefix 'poly-' (like polyethylene from ethylene). However, many natural polymers have unique names that don't mention the monomer. Similarly, many synthetic polymers are known by their commercial brand names. Can you think of any examples?