Your child's high school transcript is a record of all the classes they've taken in high school and the grades they've received. It may also include their standardized test scores and academic honors.
Most colleges require official high school transcripts from students as part of their application. Official transcripts usually have to be sent to the college directly from your child's school.
Your child's school counselor can tell you how to request an official transcript from your school; they can also help you get an unofficial transcript for your records.