[LJ Genie] What is this called?

[maradydd]

Dear LJ Genie,

Here is a picture of an audio cable:



I know that I can go to Radio Shack and buy a screw-together or snap-together end for an audio cable, but the friend on whose behalf I am asking doesn't need an audio cable; he needs to provide more mechanical stability for a join, and layered heat-shrink tubing doesn't look nice. Is there a name for the thick plastic part of the cable that one holds onto while inserting the male end into a socket, such that I could search for it on digi-key?

ETA: It's a strain relief boot. Thanks, grepmaster and tikiking!