PE stands for polyethylene which is a material used for braided line.
You'll commonly see braid advertising the number of strands used in the weave of the line and they'll be referred to as 4 or 8 carrier, now the most common with 12 available in premium line
More strands achieve a rounder profile and a smoother finish and ideally a higher breaking strain.
To make it easier for the consumer, most brands (e.g Daiwa with J-Braid & Sunline with Super PE) market their lines with a breaking strain that’s 10 times the PE rating – 10 X (PE) 5 = 50lb. Although, in most cases these lines will break well above the advertised breaking strain.