An article is a word that accompanies a noun.
Articles provide some basic information about the noun they modify.
An article tells us, for example, that the object or person it refers to is a specific one, i.e., one that the speakers have mentioned previously. In this case, it is said to be a definite article. Articles can also tell us that the object or person is not a specific one, but rather just any one of the existing objects named by the noun. These are called indefinite articles. You should take a taxi and go see her.