What are python modules? Name some commonly used built-in modules in Python?

If you are coming from Java background you might be knowing about packages and APIs which are nothing but a normal package already being developed with the JDK.Now what they do they are used to do some special things in programming.Such as java.io.Math which is used for Mathematical calculations in java.Similarly in python we have modules and modules are also same as packages i.e they are python file which are imported in other files to get the functionality of that file to the file in which we are currently working.we can easily create our own modules in python very easily by making a python file.There are a lot of python modules such as time,os,sys which are used to perform different utilities.