עֹרֶף ʻôreph (H6203)

the nape or back of the neck (as declining); hence, the back generally (whether literal or figurative)

1) neck, back of the neck, back 1a) back of the neck 1a1) of fleeing foe 1a2) of apostasy (fig.) 1b) stiff of neck, obstinate (fig.)

from עָרַף (H6202);