What is the meaning of Skewness?

The property of being skew.

A measure of the asymmetry of the probability distribution of a real-valued random variable; is the third standardized moment, defined as ${\displaystyle \scriptstyle \gamma _{1}={\frac {\mu _{3}}{\sigma ^{3}}},\!}$ where ${\displaystyle \mu _{3}}$ is the third moment about the mean and ${\displaystyle \sigma }$ is the standard deviation.

Source: wiktionary.org