the GNU version of the Collaborative International Dictionary of English
adj. Not set; not fixed or appointed.
The Century Dictionary and Cyclopedia
Not set; not placed. Unplanted.
Not sunk below the horizon, as the sun.
Not fixed; unappointed. See steven.
Not placed in a setting; unmounted: as, unset gems.
Not set, as a broken limb.
Word Usage
"It's also possible to perform additional tasks when working with the "isset ()" and "unset ()" PHP functions, but in this case by using another set of complementary functions, called "__isset ()" and "__unset ()" respectively."