What is the difference between Compile and Submit?

Every problem page has two buttons:

• Compile and Run
  • When you click this button, the code that you have submitted is tested against the sample input and sample output.
  • This is meant for you to check whether your code is working correctly when it is evaluated against the sample test cases.
• Submit
  • When you click this button, your code is evaluated against internal test cases.
  • These extensive test cases take your program through rigorous checks to ensure that the code passes all the relevant test cases.