Broad Reach is defined as a heading of about 45° either to the left or to the right of the direction in which the wind is blowing.
Broad Reach can be used to describe the heading of a ship - I.E. the ship is heading ~45° off to either side of the wind's direction.
It can also be used to describe the position of an object relative to the ship. For example, if an enemy ship is at Broad Reach, we must turn ~45° off the wind's direction in order to head directly towards it.
If the wind is blowing from east to west, as occurs often in the Caribbean, Broad Reach would be both North-West (NW) and South-West (SW). Of course, since wind direction tends to change, the direction of Broad Reach changes with it. It will always be 45° off the wind's current direction, whereever the wind is heading at the time.
Broad Reach is considered at least a "comfortable" Point of Sailing for all ships, regardless of Type. Any ship can develop at least some speed when heading in this direction. Some ships, especially the mid-sized ones, will sail fastest at this heading, but no ship will have any particular trouble traveling at Broad Reach.
In the original game, all ships will develop reasonable speed when heading at Broad Reach.
Most of the larger Square Rigged ships (Merchantman and upwards) actually have Broad Reach as their Best Point Of Sailing, meaning they will achieve top speed when taking this heading. The Cargo Fluyt is in fact the only Square Rigged ship that does not sail best at Broad Reach.
Sid Meier's Pirates! (2004)Edit
Small-to-Mid-sized vessels, such as the Brig Class and Sloop Class, have Broad Reach as their Best Point Of Sailing. While both ships will do well in other headings too, Broad Reach is by far their best for attaining maximum speed. The Pinnace Class doesn't perform as well here as at wider angles like Beam Reach, but their incredible speed means that they will still outpace most ships even at Broad Reach.
Larger ships, especially warships like the Frigate Class and Combat Galleon Class have Broad Reach as the widest angle at which they still hold a good speed. Veering beyond this angle will begin to slow them down considerably. While the Pirate-O-Pedia lists Broad Reach as one of these ships' Best Points of Sailing, both will actually prefer Running Broad Reach to attain maximum speed.
Interestingly enough, both the Fluyt Class and Merchantman Class are specifically listed as not performing as well at Broad Reach as at either narrower angles (Running Broad Reach) and wider angles (Broad Beam Reach). However, they do not benefit much from turning to their Best Points of Sailing anyway, meaning that they will still be comfortable at Broad Reach.