I suggest to remove (or even blacklist) the projection tag. The problem with this tag is that the word projection is used in many various meanings in mathematics. There is projection map in geometry and in linear algebra. In linear algebra we also have projection matrix. The term projection is ...

Should we have a black-scholes tag? We have quite a few related questions that are currently spread across different nearby tags (such as stochastic-calculus, pde, and finance) but no one tag to unite them.