This is the 3757th most frequent Catalan word.
aixó
"This."
In this sentence, 'això' functions as a demonstrative pronoun, referring to the specific item being discussed, namely 'my favorite book'.
Això és el meu llibre preferit.
This is my favorite book.
Here, 'això' acts as a demonstrative pronoun to indicate the matter or concept that the speaker is having trouble understanding.
Això no ho entenc bé.
I don't understand this well.
In this instance, 'això' represents a previous notion or idea that would have influenced the speaker's actions.