The offset distance from the start of the previous track so that the head has time to switch from top of platter to bottom of platter and be at the start of the new track. See cylinder skew.
"head skew." YourDictionary, n.d. Web. 16 May 2018. <http://www.yourdictionary.com/head-skew>.
head skew. (n.d.). Retrieved May 16th, 2018, from http://www.yourdictionary.com/head-skew