When we talk about PASSIVE RFID tags there are 2 basic types of communication used with the passive RFID tag.

Backscatter

Induction Coupling

as you may have guessed induction coupling is used for induction coiled antenna type while backstatter is (in general)the communication method for RFID tags with UHF antenna

Backscatter RFID tags reflect the RFID Readers own RF signal back to the reader, only now the signal has been modified with the tag data embedded and the RF signal is modulated . instead of a constant RF wave it's now an On/Off signal



Inductive Coupling is generally used by LF and HF RFID Tags .
How it works :

The RFID Reader/Interrogator uses current to generate a magnetic field .
As the RFID tag enters this magnetic field generated by RFID Reader
the current is transfered and powers the RFID Chip . The RFID tag/Chip switches the impedance of the RFID tag's antenna , causing modulation of the magnetic field thereby joining(coupling) the RFID tag and RFID Reader. this modulated signal is de-modulated by the RFID Reader and the data is extracted or collected