"Nail clippers" are the tool that you use to cut your fingernails. There's also a larger version for cutting your toenails.

Other types of tools are also called "clippers". For example:

• Hair clippers are a machine that cuts hair. Sometimes the scissors that a barber uses are also called "hair clippers".
• Hedge clippers are used to prune bushes and hedges.
• Wire clippers are a small tool that cuts wires.
• Bolt clippers are a big tool that you can use to cut open a padlock or a chain.

You use the word "clippers" with an "s", even when you're just talking about one item.