Looks transparent to me. pdes must be "pipe descriptors". ifs probably refers to the IFS concept in the shell; it may have come from getenv("IFS"). wordexp is described as influenced by IFS, and this function may have to look at that variable even though it's calling an external program to pass it different arguments (which is a bit weird at first glance: the program seems dedicated to the purpose; why can't it handle that aspect internally). flags is probably coming from the wordexp flags argument; it's being tested using the documented bitmask constants in the API.

Basically the coder here didn't just make up identifiers; they have connections to pervasive Unix concepts.