Here are definitions from International Monetary Fund (IMF) for Gross Domestic Product (GDP) related terms:

Gross domestic product (GDP) is the most commonly used single measure of a country’s overall economic activity. It represents the total value at constant prices of final goods and services produced within a country during a specified time period, such as one year.

GDP per capita
GDP per capita is GDP divided by population.

GDP Purchasing Power Parity (GDP PPP) is gross domestic product converted to international dollars using purchasing power parity rates. The Purchasing-power-parity (PPP) exchange rate (or conversion rate) between two countries is the rate at which the currency of one country needs to be converted into that of a second country to ensure that a given amount of the first country’s currency will purchase the same volume of goods and services in the second country as it does in the first.

GDP PPP per capita
GDP PPP per capita is GDP on a purchasing power parity basis divided by population.

Real GDP Growth
Real GDP Growth of a country is computed from GDP reported in its national currency. It is different from the GDP growth of a country GDP in the US dollars.

Developed vs Developing Nations
IMF uses the following criterion to classify the world into advanced economies and emerging market and developing economies:
(1) per capita income level,
(3) degree of integration into the global financial system.