Y for X provides you with a group of companies that offer solutions similar to a marquee company (Y) but operate in a different sector/industry (X).
For example, Uber for X includes "Uber for Drivers", "Uber for Photographers", etc.
Each feed will have companies that offer solutions similar to Uber but are customized for Drivers, Photographers, etc.
You can access Y for X Practice Area from the Home page under "Sectors, Geos, Teams & more (Coverage Areas) > Y for X"