Point of aim can mean two different things: when gap shooting, the point of aim is the spot on the target where you aim the arrow, which may be below, on, or above the spot you want to hit. You focus on the spot you want to hit; not the point of aim or the tip of the arrow. The second meaning is an aiming method where you do focus on the tip of the arrow. Most people do not use the point of aim aiming method these days.
Gap shooting is an aiming method where you use the arrow point to aim the shot. Depending on how far away the target is, you pick a spot above, on, or below the spot you want to hit and place the arrow point on that spot in your out of focus peripheral vision. The distance between the aiming point and the spot you want to hit is the gap. You determine the gaps for all distances you plan to shoot, usually in 5 yard increments, by shooting arrows from those distances aimed at the spot you want to hit and measuring the distance the arrows hit above or below that spot. In the field, you estimate the distance to your target and hold the arrow above, on, or below the spot you want to hit by the gap you previously determined for the distance you estimated.
Split vision is a type of gap shooting named by Howard Hill. Rather than measuring gaps, he shot many times at all the distances he planned to shoot until he had a good feeling for what the gaps should be, without having to put numbers on them. Then whenever he shot, he would hold over, on, or under the target by the gap that felt right to him. He always focused on the target, with the arrow point in his out of focus peripheral vision. This is very close to instinctive shooting, except that aiming points are not used in instinctive shooting. Aiming points can be useful for a second shot if you miss the first, because it will give you a reference point if you want to shoot longer or shorter on the second shot. Howard evolved from pure instinctive shooting to split vision early on in his career.
Point on distance is the distance where your gap is zero; i.e. you put your arrow point on the spot you want to hit.