To make partial or minor changes to something, typically so as to improve it or to make it less extreme. The teacher decided to modify the lesson plan to better suit the needs of her students.
To change the form or qualities of; alter partially; amend. The company had to modify its policies to comply with new regulations.
To limit or qualify the meaning of, as a grammatical modifier. In the sentence 'The red car is fast,' the word 'red' is used to modify 'car.'