Difference between 'urbe' and 'oppidum'?

1. What is the difference between Urbs and Urbe?
2. What is the meaning of Oppidum?

What is the difference between Urbs and Urbe?

urbs is the singular, feminine, nominative form used for the subject of sentences or as a subject complement. For example, urbs est magna, 'the city is large'. urbe is ablative case and would appear with prepositions, ab, in, de and ex, most likely, e.g. in urbe habitamus, 'we live in the city'.

What is the meaning of Oppidum?

: an ancient Roman provincial town lacking self-government. especially : one having walls and fortifications and serving as a provincial strong point.