Esquire

Esquire (abbreviated Esq.) is a term denoting social status. Always rather vague in its extent, the term carries little social distinction today. Nonetheless, its use as a postnominal honorific remains fairly common, particularly in the United States, where it is used to indicate licensed attorneys.
The term is British in origin. Ultimately deriving from the medieval squires who assisted knights, the term came to be used automatically by men of gentle birth. Thus use of the word postnominally represented nothing more than the claim to be a gentleman. More specifically, though, a distinction was made between men of the upper and lower gentry, who were "esquires" and "gentlemen" respectively (between, for example, "Thomas Smith, Esq." and "William Jones, Gent."). A late example of this distinction is in the list of subscribers to The History of Elton, by the Rev. Rose Fuller Whistler, published in 1882, which clearly distinguishes between subscribers designated "Mr" (another way of indicating gentlemen) and those allowed "Esquire."
Thus, practically speaking, the term "esquire" may be appended to the name of any man not possessing a higher title (such as that of knighthood or peerage) or a clerical one. In practice, however, "esquire" in the US is most commonly used by lawyers in a professional capacity; it has come to be associated by many Americans solely with the legal profession.
Regardless of who it is applied to, the term "Esq." should not be used when talking about oneself, or in directly addressing somebody else. Rather, it is used in third-person contexts, such as envelope addresses.