The document discusses the Amazon rainforest, the largest tropical rainforest in the world. It spans 9 countries in South America and covers over 5.5 million square kilometers. The Amazon river runs through the forest and at over 6,840 km is the second longest river in the world after the Nile. Around 400-500 indigenous tribes call the Amazon home and 50 tribes have had no contact with the outside world. The ecosystem is incredibly biodiverse with over 40,000 plant species, 1,300 bird species, and many other animals.