a) when an adjective is used as a noun. For example, lo azul would be used to say "the blue thing" or "that which is blue."
b) as the demonstrative pronouns esto, eso and aquello. They are used to refer to an object whose identity is unknown or to an object or concept rather than a thing.
c) as the neuter direct object lo, such as in the sentence quiero comprarlo, "I want to buy it."
Spanish also has a neuter pronoun, ello, that means "it," although its use is nearly obsolete and is found primarily in literature.
In English, the personal singular neuter pronoun is "it."

