平面向量中,将方向相同或相反的非零向量定义为平行向量,平行向量也叫做共线向量.也就是说平面几何中的“平行线段(直线)、共线线段(包括重合线段)”在平面向量内看做一个概念,平行即共线,共线即平行.平面向量中“∥”与平面几何中“∥”涵义不同,即AB∥CD与AB∥CD是不等价的. In a plane vector, non-zero vectors of the same or opposite direction are defined as parallel vectors, and parallel vectors are also called collinear vectors. That is to say, “parallel line segments (straight lines) and collinear line segments (including coincident line segments)” in plane geometry are In the plane vector, we see a concept that is parallel and collinear, and the collinear lines are parallel. The “∥” in the plane vector is different from the “∥” in plane geometry, that is, AB∥CD and AB∥CD are not equivalent.