The term `district judge` as specified by the Constitution of India refers to a Judge who oversees legal proceedings in a District Court.

Option 1, `Chief Presidency Magistrate`, is not included as they operate in a metropolitan city`s magisterial court and not in district courts. However, they can still be considered district judges as they hold a similar position in metropolitan areas.

Option 2, `Sessions Judge`, is also part of the district system; they hold court sessions and are responsible for hearing grave criminal offenses. Therefore, they can be termed district judges.

Option 3, `Tribunal Judge`, is the correct answer as these judges oversee specific areas of law and handle specialized or technical matters. Their activities are not confined to a specific geographical jurisdiction like a district, hence are not considered district judges.

Option 4, `Chief Judge of a Small Cause Court`, could be considered under the term district judge as small cause courts handle minor civil matters and these courts come under the jurisdiction of district courts.