Impact Zone

 Inconsistent
A surf condition in which waves don't arrive frequently or predictably, and there are long, uncertain waits between sets.

Indy Grab
Backside maneuver where surfer grabs the board between his legs on the toe-side rail. Also describes the location of the grab.

Innit 
Used in place of isn't it.

Inside
The takeoff position on a wave closest to the curl than any other surfer. Also "caught inside": being located inshore of the breaking waves or inside the impact zone or break line.

The takeoff position on a wave closest to the curl than any other surfer. Also "caught inside": being located inshore of the breaking waves or inside the impact zone or break line.

In Surf We Trust
Popular mantra spoken by many surfers when asked why they surf.

Interval
See swell period.

Isobath
A line connecting points of equal depth below a datum to measure bathymetry and an Isobar when used to depict Low and High Atmospheric Pressure readings.

It's All Good
When all the elements involved in getting optimum waves - wind, tide, swell direction all come together. Also applied to any situation when multiple factors have to come together to ensure the best of anything can occur.

Isobars
Lines of equal atmospheric pressure on a weather chart. The closer the lines are together, the faster the wind blows within the isobars.