PIT stands for Passive Integrated Transponder, a name created by Earl Prentice for low frequency RFID tags. 

PIT tags are small electronic circuits sealed in a glass capsule.  They have no internal power supply and are inductively charged by magnetic fields that power the tag to transmit a unique identifying number.

Since low frequency PIT tags use magnetic fields for power and communication the signals will go through any non-metallic material such as water, wood, soil, plastic, cloth, animal tissue, and ceramics.