Impacted majors
An impacted major is a major for which more students apply for than the school can accommodate. It is a classic example of when Demand exceeds Supply. When this occurs, the major becomes impacted and therefore is susceptible to higher standards of admission.
For example: Lets assume there's a school whose minimum requirements are SATs of 1100 and a GPA of 3.0.
If a person applies to an impacted major, the school can raise the minimum requirements as much as needed in order to weed out the students it is unable to accommodate.
In some cases, it is a better idea to apply to a school as "Undeclared".
For example:
If the school implements requirements of SATs of 1300 and a GPA of 3.4 for the impacted major, it would be better to apply as "Undeclared" if the student only meets the minimum requirements. The student will then have a better chance of being accepted and generally has the option of changing his/her major at a later date.