This is the 124th most frequent Spanish word.
todas
"Todas" means "all" or "every" (feminine plural).
In this sentence, 'todas' is used as a pronoun to refer to 'all' in feminine plural, indicating every person included in a group referred by a feminine noun.
Todas las personas están invitadas a la reunión.
All the people are invited to the meeting.
Here, 'todas' serves as an adjective modifying the noun 'cartas', which is a feminine plural noun, to mean 'every one'.
Ella leyó todas las cartas que recibió.
She read all the letters she received.
In this example, 'todas' is used as a standalone pronoun referring to all feminine plural entities previously mentioned.