The word “demos” had three different definitions during the archaic period. They were used to define either 1) the division of land into smaller sections 2) a classification of Athenian citizens, and 3) a group of troublesome individuals.
1) In 570 BC, Cleisthene developed a reformation of politics and social standings in Athens by dividing Athens and areas of the Attic peninsula into ten smaller sections of land which was referred to as “demos”. This was done to break up three hostile faction groups known as “men of the plains”, “men of the coast" and “men of the Hill”, that were preventing Athens from reaching general censuses among men in political matters.
2) Sparta was an aristocratic city and only gave few select men the title of citizens with political rights. Athens, on the other hand, was a democratic society that viewed any free, native born male as citizens with political rights. This form of democracy was called "demos".
3) Thucydides, a historian, Aristocrat and general in an ill fated war against Sparta during the Peloponnesian Wars, began writing skewed events of the war. Although Pericles, a fellow Aristocrat, died within 2 short years after the war began, Thucydides gave credit to Pericles for his greatness in his ability to keep the Demagogue mob, interchangeably referred to as "demos", from creating havoc and destruction in Athens during the war.
References
Cleishenses 570 BC Retreived from http://www.pbs.org/empires/thegreeks/characters/cleisthenes_p1.html
Brand, Peter J. (2010:1-36) Athens & Sparta: Democracy vs. Dictatorship.