# What is the definition of head in Mathematica? [closed]

I know (by practice) what a head is, but I am unable to find the appropriate words to actually define it. I would like to see a precise definition of head using the appropriate technical words involved. Hopefully, this should provide me with a better understanding of how Mathematica works.

• Note that as stated in the documentation, "Heads need not be symbols", e.g., FixedPointList[Head, f[x][y][z]] // Most returns {f[x][y][z], f[x][y], f[x], f, Symbol} – Bob Hanlon Sep 25 '15 at 21:39
• An answer may be found in the first tutoria,l Everything Is an Expression, linked in the documentation for Head. – Michael E2 Sep 26 '15 at 1:30