What's different between pending and blocking in signal concept?

Dear colleagues.

I am reading Stevens' book. In his book (apue), a signal concept is
introduced well, however I can't understand the meaning (pending and
blocking) in page 283. In the book, he wrote that during the time
between the generation of a signal and its delivery, the signal is said
to be pending. Well, I can understand above sentance. But, what's
meanning blocking?

Does anyone know different between pending and blocking? Please,
explain the difference.