After searching what defines many of the kinds of weapons in the PHB, I have found that the definition of pike and spear tends to be a placeholder for "pointed polearm" with their size being the only difference between the two. As defined, a pike would include all heavy pointed sticks unable to be thrown (such as halberds, glaives, etc) and spears would be any polearm that keeps the ability to be thrown (such as trident and arguably javelin).
That said, there are still many kinds of pikes and spears left unlisted in the PHB, leaving the definition, to me, as broad as saying "single-handed sword" or "two-handed sword."
What I would like to know from the community is if there are any specified differences, such as tip shape or size, that would single these out as "a pike" or "a spear"? Or is this liberty left specifically to the player's imagination?