Origin story
When Parvati embraced Shiva, their forms merged into one body, half male and half female. The image of Ardhanareeshwara reveals that the divine masculine and feminine are not two things set against each other but a single whole.
The right side is Shiva with matted hair and trident, the left is Parvati with a mirror and graceful ornament. The form is a meditation on consciousness and energy, and it is invoked wherever devotees seek harmony between strength and tenderness.
Source: Wikipedia: Ardhanarishvara — https://en.wikipedia.org/wiki/Ardhanarishvara