Joint compound is used to fill in creases and joints between pieces of drywall. It can also be used to repair relatively large holes in a wall. In contrast, spackle is used to repair smaller holes caused by nails or screws.
One difference between joint compound and spackle is drying time. Spackle will dry much faster than joint compound and usually requires a single application. Joint compound, however, should be applied in two or three layers.
Another difference between the two is in their compositions. Spackle is a plaster made out of gypsum and glue; whereas, joint compound is composed of water, limestone, hydrated obsidian, foam rubber and clay materials. Additionally, because of the inclusion of water in joint compound, this material has a tendency to shrink as it dries, which may cause the compound to crack. This is why multiple coats are required. Spackle, on the other hand, will not shrink as it dries.
The name spackle originally referred to a product created by the Muralo Company that was based out of New Jersey. The product was patented in 1928 and was originally a powder that was mixed with water in order to create a paste prior to application.