What does the first quartile mean?

First quartile meaning:

The first quartile is the median of the lower half of the data set. It is denoted by $Q_1$.

$25\%$ of the data smaller and $75\%$ of the data is larger than the first quartile.

Example: $1,2,3,4,4,5,7,8,8,9,10$

The lower half of the data set is $1,2,3,4,4$ and the median of the lower half is $3$.

Hence, the first quartile of the data set is $Q_1=3$.

Hence,the meaning of first quartile is explained.