| ICED | To execute a wave perfectly. |
| IMPACT ZONE | The point at which the swell is breaking most heavily and frequently. |
| INDICATOR | An offshore deep-water reef or bank. Only a big swell or big set will break on this, so it acts as a good indicator of something big approaching. |
| INFUSIONS | When 2 surfers collide. |
| INSIDE | Shoreward of a breaking wave or set (as in 'caught inside'), or an expression for life in the tube. the inside rail is the one nearest the wave face. |
| INVERTED AERIALS | Airborne and upside down. |