The numbers in the name of a board or sail are more than just model numbers -- they are measurements. A New School 180 board, for instance, has a volume of 180 Liters. If a sail is a "5.5" it means it has a surface area of 5.5 square meters.
Board length and width seems to get measured in centimeters.
It seems that surfers like metric.
Speed can be measured in miles per hour, kilometers per hour, or nautical miles per hour (knots). One knot is equal to about 1.15 mph. One kph is equal to about 0.62 mph.
Hint: google has a built-in calculator which understands units. For instance, you can type 5.5 square meters in square feet into google and click search. Another example: 20 mph in knots
Cardinal wind direction is indicated by origin. A north wind comes from the northern direction and blows south. An east wind blows from the east towards the west.
However, it seems that an offshore wind blows from the land towards sea. An onshore wind blows from the direction of the sea on to land. Online I've seen a few folks get this wrong.
Incidentally, offshore winds are considered dangerous because they blow you away from safety. If you lose a fin, you'll have a very difficult time reaching shore.