This is the 14351st most frequent Russian word.
открытом
"Открытом" means "open" (in the prepositional case).
Here, 'открытом режиме' means 'open mode,' indicating a transparent or public discussion format, with 'открытом' modifying 'режиме'.
Сегодня обсуждение пройдет в открытом режиме.
Today the discussion will be conducted in open mode.
In this case, 'открытом пространстве' refers to an 'open space,' where 'открытом' describes the noun 'пространстве,' implying it is not enclosed or surrounded.
Мы оказались на открытом пространстве посреди леса.
We found ourselves in an open space in the middle of the forest.
The phrase 'открытом воздухе' means 'outdoors,' where 'открытом' modifies 'воздухе' to convey the idea of an open-air setting.