Modifier
A modifier is a word or group of words that describes or gives more information about something else in a sentence.
Example:
The small dog barked.
small = modifier because it describes the dog.
Misplaced modifier
A modifier should be placed close to what it describes.
❌ Running down the street, the backpack fell off Maya.
This makes it sound like the backpack was running.
✅ Running down the street, Maya felt her backpack fall off.
Now running down the street clearly describes Maya.