In sailing, tide refers to the vertical rise and fall of the sea surface, driven by gravitational forces of the Moon and Sun, changing water depth. It is distinct from tidal current, which is the horizontal flow of water (ebb/flood). Key terms include high/low water, spring/neap tides, and slack water.

Key tidal terms every sailor should know:
Tidal Range: The vertical distance between high tide and the following low tide.

Flood Tide/Current: The incoming tide, where water flows toward the shore or up a river.

Ebb Tide/Current: The outgoing tide, where water flows away from the shore.

Slack Tide/Water: A short period between flood and ebb, where water is not moving horizontally.

Spring Tides: Occur during full/new moons; highest high tides and lowest low tides, resulting in stronger currents.

Neap Tides: Occur during quarter moons; minimal difference between high/low tides, resulting in weaker currents.

Chart Datum: The reference level on charts (usually lowest low water) to which tidal heights are added.

Rule of Twelfths: A quick rule of thumb for estimating the height of the tide at any given hour.