adverb
on the way, en route
A2
Unterwegs is an adverb meaning 'on the way' or 'en route', used to indicate someone or something is traveling or away from home (e.g., Ich bin unterwegs). It is not inflected as a noun, takes no auxiliary by itself; often used with sein. No specific preposition required.
Examples
Die Familie fuhr weiter, obwohl sie unterwegs einen platten Reifen bemerkten.
The family kept driving, although they noticed a flat tire while they were on the road.
Unterwegs habe ich viele Fotos gemacht.
I took many photos while en route.
Ich bin gerade unterwegs und kann nicht lange sprechen.
I'm on the way right now and can't talk for long.
Details
Mnemonics
a person walking down a road with a sign 'unterwegs'
unterwegs ~ 'under-ways' -> under the ways: moving
Notes
Adverb meaning 'while traveling' or 'on the way'. Common in everyday speech.