A Bikini covers 3 rows* of hair outside of the bikini line within the inner thighs (and does not treat past a typical underwear line towards the pubic area). 

An Extended Bikini covers the same area as a regular Bikini treatment, plus a small section within the underwear line, consisting of two rows inside the sides of the underwear line and from the front of the waistband. Note that it does not extend to the behind. 

*A row is classified as one line of pulses.