A smudge is a messy mark or streak made when something gets smeared or rubbed, usually accidentally. When you're drawing with charcoal and accidentally drag your hand across the page, you create a smudge. When someone with dirty fingers touches a clean window, they leave smudges behind.

The word can also be a verb: you can smudge your homework by touching the wet ink before it dries, or smudge your glasses with fingerprints. Artists sometimes smudge pencil or charcoal drawings on purpose, using their fingers or special tools to blend and soften lines into shadows.

Smudge suggests something that was clean or clear but now has an unwanted blur or streak across it. A smudge on your shirt might be small, but it's noticeable enough to bother you. Unlike a stain, which soaks in, a smudge sits on the surface and can often be wiped away. When you clean a mirror, you're removing all those smudges so you can see your reflection clearly again.