This is a common world you are listen in computer and web applications programming . Asynchronous is the opposite of word synchronous , which means existing or occurring at the same time . The its obvious asynchronous meaning not occurring same time . Word “async” is abbriviation of Asynchronous .
This term is used to control timings to loading something in program. When you set a script loading as Asynchronous , in program, then it means your program will not wait for loading the script and other codes are executed .
Where Asynchronous are usable
Asynchronous or Asynchrony or async is useful to speed up loading of programs ,because program don’t wait for finish the script loading .
When you execute web scripts asynchronously ,your webpage start loading on even slow internet connections this is a major benefit.
These type of timing controls are less secure . This is the reason ,banking website and online payment site etc are not preferred Asynchronously loading there programs ,scripts or function .