The explanation of tangent in middle school is rather vague. The explanation in high school textbooks is to take two points on the curve and connect them. This is called secant. Then one of the points approaches the other point infinitely, that is, the secant is also moving, and then the two points coincide. The resulting straight line is a tangent. Junior high school should only involve the tangent of the circle. The tangent of an element has only one intersection with the element.