A School Profile is a record put together by your school (usually a brochure or flyer) that includes information about the student body and the types of classes offered by your school, such as AP, DC, IB, etc. It usually lists figures like graduation rates and other notable facts about the school, though each one is different. The School Profile should be submitted by your counselor through the School Report, although you can also upload this document yourself from the Academic page of your application.
Your GPA might be great but it's not just about a high number, it’s also about how rigorous your course selections are in comparison to what courses your school offers. Let me explain: If your school offers 15 AP/dual credit options, but you only took a few of those, you’re not showing that you’ve pushed yourself. Admissions officers are looking for a rigorous course selection and want to see that the advanced courses increase as you move through high school; this is essentially preparing you for the rigor of college.
Admissions officers know this information about your school because they received a School Profile with your transcript.