why does the book Pre-Calculus 12 have 12 at the end

The number 12 in the title "Pre-Calculus 12" refers to the grade level for which the book is intended. In many Canadian provinces, including British Columbia where the book is commonly used, grade 12 is the final year of secondary school. Therefore, "Pre-Calculus 12" is a pre-calculus textbook designed for students in their final year of high school.