What is a proper definition of "Balanced Enrollment"?

As PISD considers revising its 2009 feeder alignment plan, I have been struggling to understand the term "Balanced Enrollment" as it applies to our Senior High schools.  In talking with a few friends, I have found the term means different things to different people.

Here is the Board of Trustees' definition, as communicated by Missy Bender in the PISD video entitled, "District in Motion: Preparing for the Feeder Alignment Transition":

"Balanced enrollment over time is not equally distributed student enrollment across the district.  It's balanced enrollment at a campus over time."

Source:http://pisdtv.pisd.edu/communications/features/9P9s3yzeipsgdDKDWDNG
Approx. Time: 03:38

I always have trouble when someone uses a term to define itself.  In my profession, that is called recursion.  This implies an "endless loop" or, more succinctly, "confusion".  But at least Missy tells us what balanced enrollment is not.

Here are ideas I received as I discussed this with some PISD friends.  Each of six people has his own definition of "Balanced Enrollment":

1. Identical enrollments across each of three Senior High campuses 
2. Aligning the enrollment so that you balance it across the 3 schools as close to the optimal use of each of their respective functional capacities as reasonably possible over time. 
3. The assignment of students to a campus in proportion to the population of students in a given attendance zone.  If 25% of the students live in an attendance zone, then 25% of the total student population should attend the Senior High in that attendance zone. 
4. A state of constant enrollment amounts over time; a steady number of students over time.
5. No wide swings in enrollment from year to year within each senior high school.  Each school should have a number at which it tends to level out at.  No large disparity in student population among the 3 senior high schools. 
6. Schools within each feeder zone level off and remain stable - and represent the percentage of the population that lives in the zone.  It is not called "equal enrollments" for a reason.

So just based on this small sample, it is no wonder that there is some confusion about what "Balanced Enrollment"' really means.  Perhaps the underlying problem is that the term "Balanced Enrollment" is a pretty nebulous concept at best.  So bear with me as I analyze it below. 

"Balance" literally means "equal distribution of amount" ( http://dictionary.reference.com/browse/balance ).  So to me, a very literal person, "balanced enrollment" means "equal distribution of students".  So it follows that "balanced enrollment" would mean "identical enrollments across three Senior High campuses".  But this is exactly the opposite of the definition offered by the Board of Trustees. 

Do you see why I am struggling here? 

Now I ask you to comment below.  What is your definition of "Balanced Enrollment"?  All I ask is that you limit your comments to the context of our Plano ISD Senior High campuses.