Which sugar is called invert sugar? Why is it called so?

(N/A) Sucrose is called invert sugar.
Naturally occurring sucrose is dextrorotatory with a specific rotation of $+66.5^{\circ}$.
Upon hydrolysis,sucrose yields an equimolar mixture of $D$-glucose and $D$-fructose.
$D$-glucose is dextrorotatory $(+52.5^{\circ})$ and $D$-fructose is strongly laevorotatory $(-92.4^{\circ})$.
The resulting mixture has a net negative rotation $(-39.9^{\circ})$,meaning the optical rotation has 'inverted' from dextrorotatory to laevorotatory.
Hence,the product is called invert sugar.