It is relative to the winds eye. That is, the winds true direction.
Measured radially, left or right, of the eye. So, we sail as few "points" from the eye of the wind as possible. As "close hauled" as we can.
Must maintain optimum angle of attack. Think of a sail, as a vertically arranged aerofoil section.
As in my above post, 1 point of wind is about 11 compass degrees.
To be able to "point" a square rigger up to 6? Nah, no way man.
Like I said, about 7 points at best. That is, 77 compass degrees off the winds true direction, then we tack or even "ware ship" (a yacht is "jibed" through the wind, a tail to the wind maneuver, a square rigger is "worn" through the wind, a frightening maneuver, much better feeling to tack nose through the wind in both types of vessel) around to the other tack. 77 degrees from the winds eye. Total tack, sailing direction change, 154 compass degrees.
All square riggers carried stay sails. Worst comes to worst, furl the squares and try to run into the wind on staysl's. But, the standing rigging still spoils air flow. Modern yachts are only stay-sail rigged.
It is the relationship between the ships center-line, and the angle of attack of the sail, to the true wind direction. Stay-sails are bent on the center-line, and the entire vessel, can be brought closer up into the eye of the wind. Squares, are bent onto yard-arms, which are arranged to pivot around the mast. And they are just not able to pull the yard-arms far enough around the mast, because of the shrouds that stay the mast sideways or athwart-ships. Square rigs are romantic, but not efficient. All sails, even to this day, are "bent" onto a mast, yard or boom. Using proper "bends and hitches", not KNOTS.
Once again, One and All.
2 masts, 13 sails. But, only 3 of them squares. All the rest, stay or boom bent, on the center-line. And even we could not point into the wind, because of the square rigging spoiling air flow over the masts, and therefore the leading edge of our "wings".
Laminar flow, Chord ratios and aspect ratios. Differentials of pressure.
Sound like aerodynamics? Sailing is. We just use the generated power, as drive not lift. But, still all the same practical applied science.