Under the Family Educational Rights and Privacy Act (FERPA) of 1974, enrolled students have access to educational records concerning them. Students are also permitted to waive (refrain from using) the rights of access to their letters of reference.
If you waive this right, that means you agree that you will not be allowed access to this particular item (the letter of reference) in your record.
Most people who write letters of recommendation feel more comfortable knowing they can write an honest assessment that is not designed to be read by the subject of the letter.
If a counselor provides a recommendation to you before you request it, note that the automatic status of that recommendation is that your rights are not waived (in other words, if you request your records from a college you applied to using that recommendation, you'll be able to see the content of that recommendation letter with the rest of your materials).