Leísmo ("using le") is a phenomenon in the Spanish language that involves using the indirect object pronoun le in place of the (standard) masculine direct object pronoun lo, especially when the direct object is animate.

Leísmo with animate objects is both common and considered correct in the dialects spoken in Spain, but ungrammatical in most others. Leísmo is always considered ungrammatical when the direct object it refers to is not an animate object.

Examples:

Veo al chico ("I see the boy") → Lo veo (standard Spanish, with lo)

Veo al chico ("I see the boy") → Le veo (leísmo, standard in Spain; other regions prefer lo veo)

Veo el árbol ("I see the tree") → Le veo (ungrammatical — the tree is not a person; should be lo veo in all varieties of Spanish)

The use of le in dialects where leísmo is standard correlates with the use of the preposition a for animate direct objects. That is, if a dialect features leísmo, le replaces masculine direct objects that would have been preceded by a if expressed in full. (For this "personal a", see: Spanish_grammar#Personal_a.)

Le is properly speaking the epicene indirect object pronoun, used for both masculine and feminine referents, whether animate or inanimate. In certain idiolects it is replaced by lo or la — dila que la quiero – but this usage is ungrammatical and considered uneducated.

Le voy a dar un regalo ("I'm giving him/her a present")

La voy a dar un regalo (supposedly "I'm giving her a present"; ungrammatical, see laísmo)

Le puse más memoria a la PC ("I got the PC more memory"; correct, even if the PC is inanimate)