What is defined as the horizontal angle at a point between true north and grid north?

The horizontal angle at a point between true north and grid north is referred to as grid convergence. Grid convergence is an important concept in navigation and cartography, as it helps map users understand how to correctly align a map with the actual geographic coordinates. True north refers to the direction along the earth's surface toward the geographic North Pole, while grid north is the direction along the grid lines of a map. Since different maps may have varying degrees of deviation from true north, understanding the grid convergence allows for accurate navigation and position fixing when using maps and compasses in the field.

This differs from magnetic declination, which measures the difference between true north and magnetic north, and is influenced by the Earth's magnetic field. Map orientation refers to how a map is aligned with the cardinal directions, while north azimuth is a specific direction measured in degrees from north, not specifically addressing the relationship between true north and grid north.