This is the 13139th most frequent Russian word.
мемориальной
Memorial.
Here, 'мемориальная' is used as an adjective describing the plaque, indicating its purpose to commemorate something.
В парке есть мемориальная доска, посвящённая героям войны.
In the park, there is a memorial plaque dedicated to war heroes.
In this sentence, 'мемориальная' describes the ceremony, indicating its nature as a commemorative event.
Мы отправились на мемориальную церемонию в честь погибших солдат.
We attended the memorial ceremony honoring fallen soldiers.
Here, 'мемориальной' modifies 'службе,' showing that the service is aimed at commemorating or remembering something.