noun, noun, used as a suffix
General noun for a quantitative or qualitative difference between things. Also used as a suffix to indicate a difference in the preceding noun (e.g., 温度差 'temperature difference').
両者の意見には大きな差がある。
There is a big difference between their opinions.
この地域では昼夜の温度差が激しい。
In this region, the temperature difference between day and night is extreme.
noun
Mathematical term for the result of subtraction.
10から7を引くと、差は3です。
If you subtract 7 from 10, the difference is 3.
違い is a more colloquial and general word for 'difference', while 差 often implies a measurable gap or margin.
格差 specifically refers to a disparity in rank, quality, or social standing, whereas 差 is a broader term for any kind of difference.
The kanji 差 is used for its meaning of 'difference' or 'disparity'. The reading さ is the native Japanese kun'yomi.