Mark making is a term used to describe the different lines, patterns, and textures we create in an artwork. It applies to any art material(s) we use on any surface(s), not only paint on canvas or pencil on paper. A dot made with a pencil, a line created with a pen, a swirl painted with a brush, these are all types of mark making.
Mark making can be loose and gestural, or structured and controlled such as hatching. Most artists work with a variety of marks in every painting, but there are some styles where you use just one, such as Pointillism.