A festive atmosphere is one that's lively and joyful, like at a holiday party or a big celebration.
The word "festive" is often used to describe things that are associated with special occasions or holidays. For example, you might see festive lights on houses during Christmas time, or hear about a city hosting a festive event, like a summer fair. Even everyday activities can be described as festive if they have a celebratory feel to them - like going to a wedding or having a big birthday party.
Having the atmosphere, decoration, or attitude of a festival, holiday, or celebration.
Example: The room was decked out in festive streamers, with flowers everywhere.
