'Squid' is a contraction of "Squirrelly Kid", and comes from So Cal racers who were also involved in the Surfer culture.
Though the term is now widely used to describe street riders of questionable cornering skill, questionable judgement in demonstrations of horsepower and braking, questionable judgement in the protective clothing worn, and very questionable judgement in his/her friends, the meaning was actually developed at the racetrack.
Back in the day before trackdays (an organized event to allow anyone with a motorcycle and the price of admission to gain familiarity with a racetrack and learn to ride faster, more safely than on the street) were common and new racers frequently had no track experience - hence their unpredictable behavior and unsteady lines led to them being labelled "squirrelly", as unpredictable surfers (or surfing conditions or surfing equipment) were also called.
From there, the term made it to the canyons of Southern California (a popular means to risk one's hide while demonstrating riding skill at speeds well over the posted limit), then out to the rest of the world that reads about So Cal in magazines and apparently strives to be just like So Cal.
"I really hate dealing with the street squids riding over their heads in the 'A' group at Buttonwillow."
"That trackday org is all about getting money from the squids who don't know better."
"Yeah, there was another squid taken off Palomar in an ambulance this morning."
At a roadracing event, a member of the officiating crew (or trackday organizer's staff) who watches the exit of corners for motorcycle (or other vehicle) crashes.
Generally, cornerworkers hold flags to regulate the racetrack - red, black, blue, yellow, green, checkered, and meatball flags - and are equipped with fire-extinguishers and radios, and a strange will to stand in the hot sun all day while people crash all around them at over 150 MPH.
"I'd like to thank my sponsors, the race officials, and the corner workers for allowing us to race here today..."
An organized event to allow anyone with a motorcycle, a reasonable set of protective gear, and the price of admission to gain familiarity with a racetrack and learn to ride faster, more safely than on the street.
Trackdays often have ambulances standing by, are run by an organizer who has corner workers who have flags to control the event, and are typically organized in 20-minute sessions of three groupings of rider skill - novice/street, intermediate, and expert/racer.
Racers use trackdays for determining setup or practice, or to bring friends to the racetrack for the first time, in the hope that they become "hooked", and can then go racing with someone else to help share expenses.
Trackdays are addictive, and can be expensive, since for about 10% of the riders, it leads to racing. And Peter Egan has noted that "roadracing motorcycles makes Heroin addiction look like a vague wish for something salty".
"Dude, if you wanna get some skills on that machine before you wad yourself into a ball in the canyons, get your hide to a trackday."
The arc described by a motorcycle's tires as it corners. On a racetrack, the proper line through any corner is determined by a number of factors: Surviveability, best setup for the next corner, best corner exit speed, and preventing other racers from passing, usually in that order. (Racing is stressful and bad decisions get made. That's racing.)
"There's a few lines that work through that combination of corners, choose one that has you sacrifice the entry to the first so you can get a good drive on the exit of the second"