What is a prerequisite?
A prerequisite is a course you must have completed before registering for another. (A co-requisite is a course must take at the same time or prior to registering for another). All prerequisites are listed in the course description for each course. Prerequisites are in place because for some courses prior knowledge of a topic is requirement.
If you don’t meet prerequisites (or co-requisite), you will not be allowed to register without a permission number.
What is "suggested preparation"?
Some departments list suggested courses to take prior to registering for another. These courses are not mandatory, but the department feels the courses help the student better prepare for the course material. Students could consult their Dean or Major Advisor before taking a course without the necessary suggested preparation courses.
I don't have the prerequisites, but I still want to take the course.
You should talk to the instructor of the course. In some situations, instructors may feel that your alternate preparation will still allow you to be successful in the course. If they permit you to take the course without the prerequisite, you will need to obtain a permission number from the instructor.
Does every course have prerequisites?
No, not all courses have prerequisites. If there is nothing listed in the course description, then the course is open to all students.