The rear taper is the section of fly lines that tapers down the belly to the running line. This section of line is vital for transferring energy into the belly.
Rear tapers come in all different lengths pertaining to the type of fishing and to the size of flies that are used in that type of fishing.
A longer rear taper helps anglers carry more line in the air more efficiently. Some distance tapers will have a longer rear taper helping them to carry more line in the air. This will load the rod deeper for a long cast.
A shorter rear taper helps the line act like a shooting head where the rod can be loaded quickly for a short quick cast. Some salt water lines have this application since quick casts are needed in the salt quite regularly.
More on rear tapers and how they affect casting in future posts so stay tuned.