Device Link Profile
Combining an input profile with an output profile produces a mathematical look-up-table (LUT) that translates colors from an input device into the best available matching colors on the output device.
When using profiles in a program such as Photoshop, this combination is held in RAM for only as long as the color transformation takes place. A Device Link profile captures this device-space to device-space transformation and saves it to disk.
The main advantage of a device link saved in this manner is some tools can then modify the profile to perform conversions differently than the default method. The most popular is Black Preservation where K-only colors sent through the profile remain K-only after conversion (the default conversion will typically yield a 4-color gray with CMY inks as well).