Hodoku explains it as follows, with reference to the picture below.
Row 2 can have its 7 in 2 different squares, both marked in green.
Row 9 can also have its 7 in 2 different squares, both marked in green.
The 7s could be in:
R2C5 and R9C6
or
R2C5 and R9C7
or
R2C7 and R9C6
Whichever combination you choose, 7 must be removed as a candidate from R3C6.
It calls this a skyscraper:
