What is a Type P light bulb?

I have a lamp that needs a new light bulb…it is calling for a 250W Type P bulb…I did a google and came up with this:

This doesn’t really help…what would happen if I used a regular (Type PS?)? I went to a hardware store and the guy there had never heard of a Type P bulb…

The shape of the bulb is mearly decorative. As long as the base threads match you can interchange any shape that fits the fixture.