headshot vs pic

headshot and pic both are nouns.

Word	Noun	Adjective	Verb	Adverb
headshot	Yes	No	No	No
pic	Yes	No	No	No

As nouns, pic is a hypernym of headshot; that is, pic is a word with a broader meaning than headshot:

headshot: a photograph of a person's head
pic: a representation of a person or scene in the form of a print or transparent slide or in digital format

Other hypernyms of headshot include exposure, photo, photograph, picture.

headshot (noun)	pic (noun)
a shot aimed at a person's head	a representation of a person or scene in the form of a print or transparent slide or in digital format
an attempt to put the soccer ball into the net by using the head	a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement
a photograph of a person's head