Hornet

Hoverfly (family Syrphidae, order Diptera)!

Hornets (like for example other wasps, bees and ants) belong to the order Hymenoptera.

Unlike Hymenoptera, flies (and thus also hoverflies), order Diptera, have only two wings plus halteres.
Furthermore, if experienced enough, you may recognize their typical eye shape and colour, mouthparts (proboscis) and short antennae.

Hoverflies are mimicking venomous insects (for example hornets, other wasps and bees).
The concept behind this Batesian mimicry is to be protected by appearing like a dangerous insect but at the same time saving the energy which would be necessary to produce venom.