L Cut: An L cut is a variant of a split edit film editing technique in which the audio from preceding scene overlaps the picture from the following scene, so that the audio cuts after the picture, and continues playing over the beginning of the next scene. 

These cuts allow editors to have the sound or dialogue of one scene linger into the next. The term derives from the “L” shape that the edit looks like on a timeline.

J Cut: A J cut is a variant of a split edit film editing technique in which the audio from a following scene overlaps the picture from the preceding scene, so that the audio portion of the later scene starts playing before its picture as a lead-in to the visual cut. Also called an audio lead or audio advance.

J-cuts are used for emotional effect as well as in smoothing transitions, keeping attention, and helping with pace. While on the surface the concept seems simple, they’re an extremely powerful technique if used effectively. The technique gets its name from the way the footage and audio appear in video editing software.