Clippers and trimmers are both devices that can be used to take the place of scissors when cutting hair. The main difference is that clippers are used for doing the bulk of a haircut, while trimmers are meant for cleaning up the edges, and doing other small work. Trimmers are typically also used for grooming facial hair such as beards and mustaches. Both clippers and trimmers are also used to groom animals, and there is a similar distinction between the two in those contexts. Dog, horse, and other animal clippers are meant to cut the bulk of the fur or hair, while trimmers are used for smaller jobs.
The common design that both clippers and trimmers share involves a set of comb-like blades that slide across each other when activated. When hair passes between these moving blades, it is cut. Both tools can be either manual or electric, though electric units are far more common. Manually operated units feature handles that must be squeezed together in order to move the blades back and forth, and they are still used in some applications. Similar units are also used to shear animals such as sheep, though electric clippers and trimmers are more commonly used with other animals like dogs and horses.
Since hair clippers and trimmers share a common design, the main differences between these devices are size and intended use. Hair clippers are large handheld devices that can be used to perform an entire haircut from start to finish. These "clipper cuts" have a wide range of different styles, and clippers can also be used to augment regular haircuts that use scissors. Electric clippers are available in both professional and consumer grade models, and can come with a variety of options and accessories. Some clippers are also able to do detail work, and some models are designed to shave closely enough to achieve a bald look.
Hair trimmers are typically scaled town versions of clippers that are meant for specialty or detail work. Clippers can be used to shave necks, do edge work, and clean up hairlines, but trimmers are specifically designed to do those jobs better and more efficiently. These smaller devices are not typically designed to cut through thick, bulky hair, but they can shave very closely and accurately. Some units are also meant for certain purposes, such as beard and mustache trimming. Other units use different blade configurations to trim ear and nose hair.