Halq means shaving of head. Shaving of the whole head of hair by the male pilgrims following the completion of Umrah or on the 3rd day of Hajj. This is more preferable based on the sunnah of Prophetﷺ. 
The sunnah of the Messenger of Allah (ﷺ) supports only Halq.
Anas b. Malik (R)reported that Allah's Messenger (ﷺ) came to Mina; he went to the Jamra and threw pebbles at it, after which he went to his lodging in Mina, and sacrificed the animal. He then called for a barber and, turning his right side to him, let him shave him; after which he tiimed his left side. He then gave (these hair) to the people. Sahih Muslim 1305
Yahya b. al-Husain reported on the authority of his grandfather that Allah's Apostle (ﷺ) invoked blessing on the occasion of the Farewell Pilgrimage three times for those who got their heads shaved and once for those who got their hair clipped. In the narration transmitted by Waki' there is no mention of the Farewell Pilgrimage. Sahih Muslim 1303 and Sahih al-Bukhari 1728 
However to do it in a different order is acceptable as the following hadith says: Narrated `Abdullah bin `Amr bin Al-`Aas(R):I witnessed the Prophet (ﷺ) when he was delivering the sermon on the Day of Nahr. A man stood up and said, "I thought that such and such was to be done before such and such. I got my hair shaved before slaughtering." (Another said), "I slaughtered the Hadi before doing the Rami." So, the people asked about many similar things. The Prophet (ﷺ) said, "Do it (now) and there is no harm in all these cases." Whenever the Prophet (ﷺ) was asked about anything on that day, he replied, "Do it (now) and there is no harm in it." Sahih al-Bukhari Vol2.:1737 and Sahih al-Bukhari Vol.1: 124