Quello is an Italian pronoun that means 'that' or 'those'. It is used to refer to something that is far from the speaker and listener, or something that has already been mentioned.
Meaning: Demonstrative pronoun meaning 'that' (singular masculine)
Quello è il mio libro preferito.
That is my favorite book.
Meaning: Demonstrative pronoun meaning 'those' (plural masculine)
Quelli sono i miei amici.
Those are my friends.
Meaning: Demonstrative pronoun meaning 'that one' (singular masculine)
I want that one!
Meaning: Demonstrative pronoun meaning 'that thing' (singular masculine)
Non so come si chiama quello.
I don't know what that thing is called.
Meaning: Demonstrative pronoun used as an interjection to express surprise or disbelief
Quello! Non ci posso credere!
Wow! I can't believe it!
A1: Quello è un libro.
That is a book.
A2: Quello è il mio amico.
That is my friend.
A2: Quella è la mia casa.
That is my house.
B1: Quello che hai detto non ha senso.
What you said doesn't make sense.
B2: Quello che mi hai detto ieri era vero.
What you told me yesterday was true.
B2: Quello che stai dicendo non corrisponde alla realtà.
What you're saying doesn't match reality.
C1: Quel che si dice in giro è che ci saranno nuove elezioni.
What's being said around is that there will be new elections.
C2: Quell'incidente ha cambiato la mia vita per sempre.
That accident changed my life forever.
C2: Quello che ho visto quella notte mi ha terrorizzato.
What I saw that night terrified me.
In Italian, quello is a demonstrative pronoun that is used to indicate something that is far away from the speaker and listener. For example, if you were pointing at a building across the street, you could say 'quello edificio' (that building) to refer to it. Quello can also be used to refer to something that has already been mentioned in a conversation, such as 'ho visto un film ieri sera. Quello era molto divertente.' (I saw a movie last night. That one was very funny.)
Quello can also be used as an adjective to modify a noun, in which case it agrees in gender and number with the noun it modifies. For example, 'quella macchina' (that car) or 'quei libri' (those books). In some cases, quello can be shortened to 'quel' when it precedes a vowel sound, such as 'quel uomo' (that man).
It's worth noting that quello is just one of several Italian pronouns that can be used to indicate distance or proximity. Other examples include questo (this), codesto (that), and ciò (that/this). The choice of which pronoun to use depends on the context and the speaker's intention.