Hi, datanewb.
The term you're asking about is read 'p+1 choose j.' If you've ever learned about permutations and combinations before, it's a combination - specifically how many ways can you pick j things from a pile containing p+1 things if order does NOT matter.
For example, consider the collection {a,b,c}. If we wanted to know how many different ways we could pick 2 things from this set it would be
.
The exact formula is given by
If you want to know where the formula comes from let me know. Does this answer your question? Let me know.
Good luck!