A gnat is a tiny flying insect, so small you might barely notice it until a whole cloud of them hovers around your face on a summer evening. Gnats are related to flies and mosquitoes, but they're much smaller, usually just a few millimeters long. Unlike mosquitoes, most gnats don't bite people, though they can be incredibly annoying as they buzz around your eyes and nose.

You'll often see gnats swarming near fruit (especially overripe bananas), houseplants, or anywhere damp and warm. Outside, they gather near ponds, streams, or compost piles. A single gnat is barely a nuisance, but gnats rarely travel alone. They form swarms that seem to follow you around, which is why people sometimes use gnat to describe any small, persistent annoyance.

The phrase strain at a gnat (or sometimes strain at a gnat and swallow a camel) means to worry excessively about tiny, unimportant problems while ignoring much bigger ones. If you spend an hour organizing your pencils by color but forget to study for tomorrow's big test, you're straining at a gnat.