Object (grammar)

An object in grammar is the target of an action, and occurs in any sentence with a transitive verb. It is an element in the clause which follows the verb, as in:
These are direct objects. The following are indirect objects:
The structure of these sentences is (S/V/O/O) where S = subject, V = verb and O = object. The first object is an "indirect object", the second is a "direct object". Notice that, in the last example, you sent a letter, not your son. The sentence makes perfect sense without the indirect object.
An equivalent sentence to the last example is:
Here some grammarians also see "son" as the indirect object ("letter" is the term which cannot be left out).p720