ρ Cassiopeiae (that's the Greek letter Rho, not a p) is a faint looking yellowish star to the right of Caph, at the top right of the "W" that is Cassiopeia. It's a variable star, with an apparent magnitude between 4.1 (hard to see in cities, easy to see in countryside) to 6.2, dim enough that it can only be seen by your naked eye in a moonless night in a rural area, impossible to see in a town.
What makes such a faint looking star notable enough to be mentioned here? It doesn't even have a traditional name!
Well you see, Rho Cassiopeia is actually fantastically large and bright. It's a G2Ia type star. G2 type is the same yellowish star as our own sun, with a similar effective temperature. But the Ia means it is a hypergiant. It's really freaking big. While it can be hard to determine exactly how big and bright due to the distance involved here, it is estimated to be about 8,100 light years away from us. Despite being so ludicrously far away, it's still bright enough to shine at the 4.5 apparent magnitude. It's one of the most luminous stars known to exist in our galaxy, emitting 550,000 times more light than our Sun. As such, it's diameter is estimated to be 450 times that of our Sun, or 630,000,000 kilometres (391,500,000 miles)!
Being so big and bright is unstable, however, and the reason for the variability in output is a result of it expelling gas. It doesn't have long (on the galactic timescale) before it will likely explode in a magnificent supernova.