EDIT Weierstrass Elliptic Function The character is used to label the Weierstrass elliptic function, a standard type of elliptic functions. The function is named after Karl Theodor Wilhelm Weierstraß, a German mathematician (1815-1897).

 jsw 

EDIT Typography The character was given a wrong Unicode-name. It is not a capital letter but a lowercase one and should therefore be named »Script Small P«.

For reasons of compatibility and stability of the world standard Unicode, wrong names are never revised in later versions of the Unicode Standard.

 jsw 

EDIT Also used in formal logic and natural language semantics to denote the Power Set function on sets.

 dan.mccloy