The document defines and discusses the concept of the centroid. The centroid of a triangle is the point of intersection of the triangle's three medians. It can be calculated using the formula that takes the average of the x-coordinates and y-coordinates of the triangle's three vertices. The centroid has several important properties: it is the center of the object, the center of gravity, and always lies inside the object. It represents the balance point of the object. The centroid, center of mass, and center of gravity are often used interchangeably for simple rigid objects with uniform density since they refer to the same point. Knowing the centroid has applications in keeping structures balanced and in calculating stresses and deflections.