A droplining is a commercial or recreational fishing technique - long fishing line is set vertically down into the water, with a series of baited fishing hooks attached to the snoods. Depending on the sea depth, droplining can be form of deep sea fishing.
Droplines are usually set down in the water column. They have a weight at the bottom of the line and a float at the top - they can be even held in the hand as the form of handline fishing. They are not usually as long as longlines and have fewer hooks. Droplines held in hand can have 1 - 5 hooks, with the weight being lowest, most often, on the sea floor. Droplines with a single hook are often rigged with a hook being the lowest.
Droplines are usually baited with whole small fishes, pieces of fish, prawns, worms etc, but in the channels with strong currents, droplines can use trolling lures with great success.
Size and the weight of fishing weight/sinker depends on the fishing depth, strength of currents, time of droplines being left in the water and size of game fish - they range from few grams to few kilograms and they are usually made of lead.
Dropline vs Trotline
Difference between droplines and trotlines is simple - droplines have a series of hooks suspended vertically in the water, whereas the trotlines have a series of hooks suspended horizontally in the water.