What it means:

A hold is a temporary status connected to your student records, placed by a campus unit (academic department, library, Bursar's Office, etc.) that wants to alert you of an action you need to take (meet with an advisor, pay a library fine, pay your tuition, etc.).

Some kinds of holds will prevent you from changing your class schedule, including enrolling in or dropping classes, until the hold is cleared.

Course enrollment failed: You have a hold on your record. The hold on your record must be removed before this transaction can be processed.

What to do:

Find out what the hold is by checking Student Center.
Follow the instructions in Student Center to resolve the reason for the hold. Then, contact the campus unit that placed the hold, to confirm that they have cleared the hold for you.
For further instructions, see: Student Center - Viewing Your Holds.

After any enrollment-related holds are cleared, you can enroll in classes. Remember to check for any holds before enrolling for future terms!

You've cleared your holds but you're still seeing an error message?
You might still be seeing an error message from the last time you attempted to add the course to your cart or enroll.

To revalidate the course in your cart:
Select the checkbox next to the course and click the Revalidate button.

If the validation error cleared, you can now enroll (even if there's still an enrollment error message). Check the checkbox next to the course and click the Enroll button.