Materials like air, water, and clear glass are called transparent. When light encounters transparent materials, almost all of it passes directly through them. Glass, for example, is transparent to all visible light.
Translucent objects allow some light to travel through them.
The opaque object does not allow light to pass through it.
As the wires of the mosquito net do not allow the light to transmit so these wires are opaque. and free space is obviously transparent.