They are eventing levels. The height increases as the level does. The dressage tests used for each level are available on the PC website!
PC level 1- 70cms or lower across the phases. Usually a lead rein class held along side an non-assisted section
PC level 2- Equivalent to BE80... max dimensions of 80cm
PC level 3- Equivalent to BE90, SJ = 95cm with the XC at 90cm
PC level 4- Equivalent to BE100, SJ max dimensions = 1.05m with XC at 1m
PC level 5- Equivalent to BE Novice, max dimensions of 1.10m
One thing I'd note is most PC Opens/ Ints are upper end versions of their BE height, whereas at the lower end it is much kinder- level 2 should be a bit smaller than a BE80 and level 1 events are designed only to encourage.