Cel shading:

A group of shading techniques that represent light and shade in a drawing or painting through blocked-in forms. Characterized by consistently sharp-edged forms of shade and light. Popular among comics, manga, and animation.

Soft shading:

A group of shading techniques that represent light and shade in a drawing or painting through smooth gradation based on the laws of light logic. Characterized by soft transitions between shade and light throughout the image.

Hatching:

Artistic technique of using closely-spaced lines to simulate shading. Hatching is usually done with parallel lines, but can also involve curved lines to illustrate contours, and parallel and intersecting lines (crosshatching) to communicate greater depth in texture and tone. A staple of older monochrome media such as engravings and woodcuts, today it is commonly associated with black-and-white cartoons.