A system in which teachers/professors can check that their students are paying attention to lectures. A mini question is posed mid-class, and students can answer it remotely using their devices. Most commonly found in US state universities.
"Dude, stop watching Pornhub, the iClicker question is on the board!"
"Oh shit, my phone's not connecting"
"Too late, the answer was C"
An iLicker is a person so enthralled with any Apple product that they feel compelled to lick it. It's a twisted french-kiss showing obsessive love for all things Apple.