Well, let's see...
What is a democracy?
A democracy is a government type that is governed by the people. For example, the people vote upon each and every issue that comes up.
A republic is a government in which people elect representatives to a Council to represent them and to vote for them in these issues. Since people are usually very busy and cannot keep up with every nuance of politics, a republic is better prepared for issues. The USA is a republic, and not a democracy as most people proclaim. Rome was also a republic, and Greece was a democracy.
To explicitly answer your question, nothing has changed! The concept of a democracy has not changed in the course of history.