Sinks are typically mounted to benches on one of two ways - either top mount, or undermount. The difference between the two is fairly basic - one sits on top of your kitchen bench, and the other sits underneath it.
What are top mount sinks?
The most common basins are top mounted sinks - also called drop-in or rimmed sinks. These basins are dropped into a hole cut into the top of a vanity or benchtop. The oversized lip of the sink forms a rim around the top of the hole, and the basin is clamped into place from underneath. Plumbing for drop-in sinks is hidden inside the cabinetry beneath them. In general, the main variations you will find with this sink type are the size and shape. In kitchens, the most common and least expensive option is stainless steel - normally with more than one tub these days.
What are undermount sinks?
Undermount sinks are similar in style but have no lip around their edge, and sit below the benchtop. These basin types are not suitable for all applications; they work best with a very solid bench surface material, such as stone or quartz. Undermount sinks are larger than the hole cut into the counter, creating an overhang into the sink bowl, and they are clamped to the benchtop from underneath. As with top mount sinks, the plumbing pipes are installed inside the cabinetry under the sink - although because undermount sinks sit lower in relation to the bench, there's typically slightly less storage space beneath them. Undermount sinks are made from the same materials as a drop-in sinks when bought separately. Some benchtops include the sink as part of the countertop - these are typically made of a moulded composite resin.
Undermount sinks are considered slightly more 'upmarket' than top mount sinks, and are popular in designer homes for their sleek look. They're also more difficult to install than top mount sinks, however they will save you time in cleaning as you can wipe your benchtop mess straight into the sink.