"What is cumulative knowledge ?"

You have probably never heard of cumulative knowledge, so seeing this title left you in an interrogative mood. 

Here I will explain what cumulative knowledge is.

First, it only applies to humans : animals does not have a culture of cumulative knowledge.

Now let's get into it : cumulative knowledge is the idea that every new thing we invent today are the results of prior invention. For example, Spacehey is the result of coding, which results of computing, which results of electricity, which results of its discovery. 

Therefore, any invention you use today is probably so advanced that no one can ever make it out of nothing. To illustrate, making a phone from nature would be impossible for one person.

To conclude, cumulative knowledge is the accumulation of inventions.