Lipper
When a surfer cranks a hard bottom turn before cutting up the face and snapping his board hard off the lip before continuing back down the face of the wave.

Liquid Smoke 
The spray that comes off the back of a wave from an offshore wind. So named because it looks like smoke at a distance. 

Local Knowledge
Knowing the slight nuances of your local surf spot; wind, tides, type of bottom (sand, rock, reef) and swell directions. Facts accumulated by mankind.

Localism
Territorial or aggressive behavior over a surf spot or a particular peak. Generally includes outsiders getting "vibed" or in extreme cases being subjected to violence.

Locals
Those who regularly surf at a particular break or area. Locals may or may not live at or near the spot, but their regular sessions mean they're accepted by the local surfing community.

Locked In  Category
To occupy the optimum position on the wave; trim, et al. To maximize a ride.

Log
Longboard, nine feet or longer. Characterized by generally thicker volume in the deck and rail areas and a spoon shaped nose.

Logger
Someone who generally rides a longboard is said to be a "logger."

Long Period Swell
Swell conditions caused by low intense pressure systems. Much more powerful and substantially bigger potential for size exists than with a trace swell.

Long-Sleeve Spring
A spring wetsuit (shorty) with long sleeves.

Longboard
Usually over 9' in length; a Tank. Their size makes them easier to paddle and get into waves sooner.

Longitude
The distance from the prime meridian (east or west), from Greenwich, England as measured in degrees along a line. Each meridian line runs in a north-south direction and starts/ends at the north/south poles.

Longshore
Water movement in the surf zone that runs parallel to the shore as a result of waves breaking at an angle to the shoreline. Synonym: Littoral Current.

Looking for Some Shade 
To surf with the sole purpose of getting shacked, tucked in the barrel or spending time in the green room.

Loot
Surf gear or the money used in buying it. Example: "I need to make some loot before I can buy a new board."

Losin' My Religion  
Idiomatic expression of complete and utter exasperation.

Low Pressure
A low pressure system is an area of relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Stormy weather is often associated with low pressure systems.

Lull
Relatively calm period between a set of waves.

Lumpy
A surfer who gets up on his board using his elbows and doesn't miss many meals (Kohler Bear).