“The Bar” simply means ‘the whole body of lawyers in the legal profession’ and it derives from the old English customs, which date back to the early 16th century. The Bar also signifies the momentous occasion, when a Law Student officially becomes a lawyer; thus joins the Bar.
Unified or Integrated Bar means that all duly licensed lawyers, who wish to practice law in some states, must be members of the State Bar of such state.
Some bar associations are responsible for regulating the legal profession within their jurisdiction; yet others are professional organizations dedicated to serving their members; in many cases, they are both.
Generally, lawyers seeking admission to a Bar must earn a Juris Doctorate Degree from a law school approved by the jurisdiction, and then pass a bar exam administered by the state. There is also a character and fitness evaluation, which includes a background check to make sure the lawyer complies with Bar’s character requirements.
A lawyer who is admitted in one state is not allowed to practice in any other state, unless he or she has been approved under doctrine of “Pro Hac Vice,” which is a Latin term and it literally means “this time only.” This legal doctrine allows an out-of-state lawyer to appear in court of another state for a particular trial, even though he or she is not licensed to practice law in the forum state.
Some states do have reciprocal agreements that allow attorneys from other states to practice without sitting for another full bar exam; such agreements differ significantly among the states.
Here is the list of Unified or Mandatory State Bars: