This is the 734th most frequent Italian word.
morti
"Morti" means "dead" or "deaths" in English.
The word 'morti' here is a substantivized adjective to indicate deceased people.
I morti vengono ricordati il giorno della commemorazione.
The dead are remembered on the day of the remembrance.
In this context, 'morti' is used as a noun to speak of people who have passed away.
I fiori per i morti sono lasciati al cimitero.
Flowers for the dead are left at the cemetery.
Here, 'morto' is used as the past participle of the verb 'morire' (to die) in a third-person singular form.