Physical vertical difference in water level, such as a waterfall drop or hydraulic head.
The drop of this waterfall is about 50 meters.
Electricity is generated using the head of the dam.
Abstract gap or disparity between two things, such as expectations and reality, or ability levels.
I struggle with the gap between ideals and reality.
There is a big disparity in ability between the two teams.
There is a big gap between expectation and reality.
He was troubled, feeling the gap between his ideals and reality.
This waterfall is a famous spot boasting a 100-meter drop.
格差 highlights an inequality in rank, income, or status, while 落差 can describe any kind of striking gap, including a physical drop.
ギャップ is a casual loanword for a gap between ideas or generations, while 落差 sounds more formal and can also mean a physical fall in height.
高低差 specifically means a difference in elevation between two points, while 落差 more often describes the drop of falling water like a waterfall.
段差 is a small step or bump you might trip on, whereas 落差 emphasizes a dramatic drop in height, as with a waterfall or steep cliff.
Compound of 落 (raku, 'fall') and 差 (sa, 'difference'). The physical sense of a water drop is primary, with the abstract gap sense developing from it.
He practiced every day to close the gap in skill between the two of them.