Glossary
Flying overtaking means you catch up with a slower vehicle and immediately then overtake the next vehicle in front. The speed is included and no further acceleration is necessary. This type of overtaking is preferable as it requires both a shorter distance and less time to be able to overtake.
A flying overtaking is better for fuel consumption and the environment than the other type of overtaking called accelerated overtaking. There you increase your speed to be able to overtake.