This is the 15062nd most frequent Russian word.
поздравительные
"Поздравительные" means "congratulatory."
Here, "поздравительные" functions as an adjective describing "открытки" (cards), specifying that they are congratulatory in nature.
Сегодня мы отправили поздравительные открытки друзьям.
Today we sent congratulatory cards to our friends.
In this sentence, "поздравительные" modifies "речи" (speeches), indicating that these speeches are meant to celebrate or congratulate.
На празднике гости обменивались поздравительными речами.
At the celebration, the guests exchanged congratulatory speeches.
The word "поздравительные" in this case describes "плакаты" (posters), showing that the posters carry congratulatory messages.