Bacon is "side pork" - the side of a pig - that has been cured and smoked. Sliced bacon has been trimmed of its rind, sliced and packaged. Slab bacon comes in one chunk that must be sliced and is somewhat cheaper than pre-sliced bacon.
"Conventional" bacon is a processed meat which is high in sodium and contains harmful preservatives such as sodium nitrites. If you choose to eat bacon, look for organic, uncured bacon such as Maverick Ranch or U.S. Wellness Meats who also make a beef bacon.