millimeter

A millimeter is a very small unit of measurement, equivalent to one thousandth of a meter.

When we talk about things that are tiny, we often use the word "millimeter" to describe them. For example, if you have a new smartphone with a super-thin screen, its thickness might be measured in millimeters - maybe it's only 5 or 6 mm thick! Or, imagine you're at an art museum looking at a tiny painting by a famous artist. If the frame is only 2 cm wide, but the artwork itself is just 1 mm thick, that's a really small scale we're talking about here. People who work with electronics, design jewelry, or study the natural world might often use millimeters to measure things that are too tiny for bigger units like inches or centimeters.