It’s a conjecture; it’s an extrapolation
based on assumptions that cannot always be proven;
reasonable people may disagree; it’s an educated guess,
a consensus of opinion, a supposition based on incomplete and uncertain evidence;
but it’s at least an X on the map.
A map purporting to show where a pirate treasure is buried must have an X on it.
See also in The book of science:
Readings in wikipedia: