Teka FlexLinea RS15 50.40 3-in-1 Installation Stainless Steel Sink is a versatile type of sink that can be installed in three different ways: inset, undermount, and flush. Inset Installation involves placing the sink into a hole cut out in the countertop. The sink is secured in place using clips or brackets attached to the underside of the countertop. Inset installation is relatively easy and is a good option for retrofitting existing countertops. 

The sink is mounted underneath the countertop, so the sink's edges are not visible. This creates a seamless look and allows easy cleaning by wiping debris directly into the sink without any obstructions. Undermount sinks are popular in modern kitchen designs and often offer a sleek and clean appearance. The installation process can be a bit more complex than inset installation and may require additional support from the cabinet structure beneath the countertop.

Flush installation involves fitting the sink so that it's level with the countertop surface. This creates a seamless and visually appealing look, as the sink appears to be an integrated part of the countertop itself. Flush installation can be trickier to achieve than other methods and may require custom fabrication of the countertop to ensure a precise fit.