We use the term warp when we measure out the threads and prepare them for braiding. Example: “I measured out a warp that was 30″ long and put it on the marudai to make a braid about half that length.”
The term comes from the weaving tradition. Warp and weft are the two basic components in weaving which turn yarns into fabric. When weaving the warp are those yarns that are kept stationary and under tension by the loom. Warp threads are lifted in a pattern to create a space for the weft yarn to be placed. Designs and structures are achieved by color placement in the warp as well as the sequence used to lift warp threads.
This is generally the same for braiding but because braids are interlaced at an oblique angle the threads are sometimes seen as warp and other times as weft.