Nazism can be best defined as the political ideology and system implemented by Adolf Hitler and the Nazi Party in Germany during the 1930s and 1940s. It was characterized by extreme nationalism, totalitarianism, and racial superiority, particularly targeting Jews and other persecuted groups. While options a) and b) do capture certain aspects of Nazism, option c) - the extermination of Jews - is the most accurate and defining characteristic of this ideology.

1. Overview of Nazism:
Nazism, also known as National Socialism, was a far-right political ideology that emerged in Germany in the aftermath of World War I. Adolf Hitler, the leader of the Nazi Party, rose to power and implemented this ideology, which aimed to establish a totalitarian state and create a racially pure German society.

2. System of Ideas and Politics:
Option a) suggests that Nazism can be defined as a system or structure of ideas about the world and politics. While this is true to some extent, it does not fully capture the unique and defining characteristics of Nazism, such as racial superiority, anti-Semitism, and the desire for territorial expansion.

3. Hitler's Determination for Greatness:
Option b) highlights Hitler's determination to make Germany a great nation. While this was indeed one of Hitler's goals, it does not encompass the broader ideology and actions of Nazism. Hitler's ambition to make Germany great was closely tied to his beliefs in racial purity, Aryan supremacy, and the need to eliminate what he perceived as "inferior" races.

4. Extermination of Jews:
Option c) - the extermination of Jews - is the most accurate and defining characteristic of Nazism. Hitler and the Nazis implemented a systematic and state-sponsored genocide known as the Holocaust, which resulted in the murder of six million Jews. This horrific act was driven by anti-Semitic beliefs that considered Jews as racially inferior and a threat to the Aryan race.

5. Hitler's Ambition of Conquering the World:
Option d) suggests that Hitler's ambition was to conquer the world. While Hitler did have ambitions of territorial expansion, including the establishment of a Greater German Reich, this goal was secondary to the ideology of racial purity and the extermination of "undesirable" populations, particularly Jews. Hitler's aim was to reshape Europe according to Nazi racial ideology rather than outright global conquest.

In conclusion, while Nazism can be defined as a system of ideas and politics, Hitler's ambition to make Germany great, and his desire for territorial expansion, the most accurate and defining characteristic of Nazism is the extermination of Jews. The Holocaust remains one of the darkest chapters in human history and serves as a stark reminder of the dangers of extremist ideologies and racial hatred.