Mist is a very dense water vapor, almost as thick as fog. Light rain can sometimes form a mist that makes it hard to see the road when you're driving.
The mist you see in the air on a damp spring morning is similar to the mist you spray when you water your plants — it's made up of tiny water droplets. As a verb, mist means "to cover with mist," so you might mist your dry plants or watch your windows mist up in the rain. Mist can also refer to a general dimness or cloudiness: "She watched through the mist of her tears."