Asynchronous Non-blocking
Asynchronous means not synchronous. Using these we can make asynchronous HTTP requests that do not wait for the server to respond. These functions continue to respond to the request for which it has already received the server response. Non-blocking functions are used in regards with I/O operations. They immediately respond with whatever data is available and keeps on running as per the requests. In case, any answer couldn’t be retrieved then the API returns immediately with an error. 

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