What is 'lasing' and why is the FBI really worried about it?

Nearly 11 aircraft a day around the country had a laser pointer aimed at them in 2013, an increasingly worrisome trend that has inspired the FBI to offer $10,000 rewards to people who help officials catch laser-shining culprits.

 

http://www.latimes.com/nation/nationnow/la-na-nn-fbi-laser-pointers-airplanes-reward-20140211,0,6735019.story