Egr is exhaust gas recirculation. If you want to know what it is like, take a mask with a hose on it and put the mask on and the other end of the hose in your pants so you can breathe in your farts..... same principle.
The system is fitted to lower the amount of fresh oxygen in the combustion chamber, reducing egts (conbustion temperature) and nox (oxides of nitrogen) emissions. With the pcv system feeding oil soaked gases from the sump (blowby gas created during combustion) back into the turbo and into the intake manifold, this hot exhaust gas (egr) bakes the oil from the pcv system onto the inside of the intake manifold until there is so much there that it basically blocks the intake manifold. If you google pictures of egr you will see the results. ... it isn't pretty. Blocking the egr and fitting a catch can stops this from happening.