Gemstones need to be cut or shaped in some way before being sold to the final link in the chain - the customer on the street who wants a piece of jewelry to wear, to show off that gemstone.
Calibrated opal - opal cut to standard dimensions. These are usually ovals, but may be cut into other shapes.
A baroque is an opal cut into an irregular shape.
Cabochon is the rounded shape used in cutting most opals.
Doublets and triplets are important words to know. A doublet is a two part stone, consisting of a thin slice of precious opal glued onto a thicker stone background. Or it could be a thin slice of opal topped with a quartz cap. A triplet is, as the name implies, a three-part stone consisting of a thin slice of precious opal glued to a thicker stone background, with a piece of clear quartz glued over the top - so the opal is sandwiched in between.
If you ever see something labeled as a Gilson opal, be aware that that is a synthetic opal. Opalite is another imitation opal.