The phrase an attorney, "of Counsel" in the United States is the title of an attorney that is employed by either a law firm or organisation who assists in litigation yet is usually neither an associate nor a partner. This title is frequently given to part-time or retired attorneys.
On the other hand, in England as well as a few other Commonwealth jurisdictions, the term "of counsel" is the correct title of a barrister who is ordered to represent a given party in litigation.
The title of "Of counsel" in the United States, bears particular ethical responsibilities. It generally refers to an attorney not actively concerned with the day-to-day workings of a law firm, who may be used in specific matters or for consultation. The title of the attorney "of counsel" stamped on the stationery of a law firm' gives it the prestige associated with a lawyer's name and reputation, while at the same time it does not need his/her full-time presence.
The term "of counsel" is used for many purposes, some of which are legitimate and proper, and some which constitute misuse of the monicker, but since the ABA gives the uncharacteristically "loose" definition of: "having a close personal relationship between firm and said attorney," it is most commonly used for: Associates who fail (or foolishly choose not) to make partner within the set period of time, but whom the firm still finds useful (advantages include less/if any of billable hour requirements, no expectation of generating business for the practice, and no need to "buy in" to partnership...while usually maintaining a steady salary, but never truly maximizing or controling their own earning potential); two lawyers/firms in similar practice areas substantively, but separate geographically and the phrase is used between a handful of lawyers at each firm to facilitate a referal relationship that does not necessitate the "of counsel" referring attorney('s firm) to do any work on the file to receive a referral fee (as required by almost all model rules of professional conduct in all states); when a firm endeavors in a large-scale, highly specific case that involves specialized knowledge an expert attorney may be brought on strictly in an "of counsel" capacity to help with that one case; an old retired lawyer who still draws money from the firm, but no longer handles any cases must still appear somewhere to alert clients they are members (conflicts still apply to "of counsel" attorneys which causes more problems than people think), but cannot take the title of "associate" or "partner" without misleading clients that retirred sponge is actually contributing beyond whatever business his/her name generates alone; and, in a similar vein, when an attorney is prestigous enough in name that a firm will be willing to compensate him financially just to associate his name with said firm, but said prestigious lawyer will actually perform no definite or easily inferred work for said firm (again, a way to mislead clients, without technically misleading clients). Best way to think of it is:the "of counsel" attorney is not an associate, not a partner, and not likely anyone who will be handling your case (unless it's one of those highly specialized cases, or it is one of those massive firms where only 30% of the associates make partner, and the rest spend their careers in limbo as "of counsel" watching 30% of each subsequent year's new hire's leap-frog over them and get rich, while they stay relatively poor, and grow old and ineffectual...