階差 is read as かいさ (kaisa) and means difference.
かいさ
kaisa
かいさすうれつ
sequence of differences
かいきゅうさべつ
classism
かい
counter for storeys and floors of a building
かいだん
stairs
しな
quality
かいそう
class
かいか
bottom of the stairs
かいじょう
top of the stairs
かいだか
height of a storey
かいちょう
gradation
かいすう
number of stairs or stories (storeys)
かいめい
name of a note in a movable do solfège system