This NFC tutorial also covers following sub topics:
How NFC Works   NFC Modulation and coding   NFC Tag vs NFC Reader   NFC Tag Types   NFC-A,NFC-B,NFC-F   difference between bluetooth,wifi,RFID and NFC   NFC Tools and Equipments

As we know ASK is the short form of Amplitude Shift Keying. In this technique, binary 1 and binary 0 is mapped as carrier and no carrier respectively. It is represented by following equation.
Output = A* cos(2*π*fc*t) for binary logic-1
While
Output = 0 for binary logic-0

As the amplitude of the RF carrier varies based on binary input, it is known as amplitude shift keying modulation.

NFC uses type-A and type-B signaling methods as defined in ISO/IEC 14443 part-2. Communication between NFC devices is half duplex with 106 kbps data rate in both the directions.

10% ASK modulation type is used in type-B PCD (Proximity Coupling Device (Reader/Writer)). As mentioned Type B signaling type uses 10% amplitude modulation of RF field for communication from reader to card with NRZ encoding. Communication from card to reader uses BPSK modulation using 847.5 KHz with NRZ-L encoding. RF field is continuously ON here.

Figure depicts waveform for the ASK modulation. Modulation index is defined as ratio of (A-B) and (A+B) as expressed below.
Modulation Index = (A-B)/(A+B) ,
Where,
A = Unmodulated signal amplitude
B = Modulated signal amplitude
Modulation Depth = B/A

10% ASK modulation means ASK modulation in which modulation index will range between 8% and 14%. The figure-1 depicts 10% ASK modulation waveform.