Physical Modeling is a type of synthesis based on the way a vibrating object (a plucked string, a struck mallet, a bowed instrument...) interacts with a resonant body (the hollow part of an acoustic guitar, the body of a hand drum). As a result, Physical Modeling allows you to not only create sounds with "real world" qualities, but to combine elements into bizarre new instruments. Bowed flutes... blown guitars... a violin played with a mallet? All are possible in the realm of PM.
Today's free sample was created via Physical Modeling in Logic's built-in Scuplture synth. It's a sort of plucked string instrument. 7 mutli-samples as 24-bit/44.1k WAV files weighing in around 6.3 MB.