I teach Geometry and according to the curriculum and textbook, I am supposed to begin the course by discussing undefined terms.
Let's look at this from the student perspective. They have been out of school for two months and at some point during that time they were bored. Most arrive for a new school year with excitement and hope. The excitement is to see old friends and meet new ones. The hope is they will learn and it will be fun.
So back to Geometry. Excited and hopeful student arrives for Geometry. The teacher begins the course by telling 'excited and hopeful' the basis for everything they will study during the year is undefined. The student is probably thinking, well at least I was excited and hopeful yesterday.
Stop the madness! Look at your curriculum, choose an activity to begin the course which will actively engage the students. Renew their hope!
Here's what I do. We begin the Geometry course with transformations (also found in the first chapter). We graph a picture on the coordinate plane then move or change the picture mathematically. We use translations, reflections, rotations and dilations. After transformations, we do Geometric constructions with a straight-edge and compass. So after two months of limited learning experiences, students come to Geometry and draw for three weeks (and develop skills we will use the rest of the year).
Let me hear what you do to make the start of your course exciting for the students.