A mark with no particular shape that is caused, usually by accident by rubbing something such as ink or dirty finger across a surface. (Cambridge Dictionary)
If ink, paint, etc. smudged or if someone smudges it, it becomes dirty or not clear because someone or something has touched it. (Cambridge Dictionary)
Cause (something) to become messily smeared by rubbing it. (Oxford Dictionaries)
A smudge is a dirty mark. (Collins Dictionary)
If you smudge a substance such as ink, paint, or make-up that has been put on a surface, you make it less neat by touching or rubbing it. (Collins Dictionary)
If you smudge a surface, you make it dirty by touching it and leaving a substance on it. (Collins Dictionary)
Vector – smudge and smear a black brush on white background, illustration clip-art.