The term "pigment" refers to a tanning process. It is used on the poorest quality hides to conceal blemishes. The resulting piece will be very durable, but not very soft.
Aniline also refers to a tanning process. It is used on the highest quality hides that have no imperfections to cover up. The resulting piece will be extremely soft, but not very durable or stain resistant.
Semi-Aniline is the third type of tanning process. It is a combination of pigment and aniline creating a piece that is midway in both the softness and durability spectrums.
The top grain is the portion of the hide on the very top. It is the outer edge of the cow's skin. It is also the softest and most expensive portion of the hide.
The split grain is the under portion of the hide that has been sliced away from the top grain. It is not as soft and is less expensive.