I am looking to hire a recent grad. He tells me he has OPT and therefore work authorization. What does that mean?

OPT, or Optional Practical Training is available to students upon completion of their degree program. A student may be authorized for 12 months of Optional Practical Training. The school attended by the student recommends the grant of employment authorization. You can employ the student who will have employment authorization pursuant to OPT and file an H-1B petition on his or her behalf.