Side-Drilled
Drilled across the narrow end rather than through the length, so a drop pearl hangs point upward.
A top-drilled drop hangs with the taper at the top and the fullest part swinging free, which is how most pearl drops are meant to sit.
Drilling through the length instead makes the pearl sit rigid on a pin, a different and more static look.
The hole is close to the surface at that end, so a top-drilled pearl is more fragile there than a fully drilled one.
When you are buying
For earrings, top-drilled pearls move and catch light. Check the metal at the hole is smooth, because a rough finding will saw at the nacre over time.
Full-Drilled
A pearl drilled all the way through so thread can pass. How every strand pearl is prepared.
Half-Drilled
A pearl drilled only partway through, so it can be cemented onto a post. How pearls are mounted in studs and rings.
Drop
Tapered at one end and rounded at the other, like a teardrop. Highly valued when the taper is symmetrical.
Hangings
Earrings that hang below the lobe, as opposed to studs that sit on it. The everyday Indian term for drop earrings.