According to the HKSAR Census and Statistic Department:
Unemployment rate refers to the proportion of unemployed persons in the labour force.
It is considered one of the key economic indicators to measure the strength of an economy. Generally, during economic expansions, the unemployment rate is lower; during economic contractions, the unemployment rate is higher.
*Note that different countries have slightly different definitions. Some countries define unemployment rate to be the ratio of unemployed person to the working age population.