Ocean waves are generated by the transfer of energy from wind to the sea surface. Their development depends on wind speed, duration, and fetch (distance over which wind acts). They are measured by significant height (Hs), period, and direction.
Wind sea vs. swell
Wind sea is locally generated, irregular and chaotic. Swell consists of waves that have travelled far from their generation area, with long periods (10–20 s) and regular appearance. Both can coexist, creating cross seas dangerous for navigation.