What is **request** here?

We have put the request in the following code.
Why, and why did we not use it in the function ?

#! /usr/bin/env python

import rospy
from std_srvs.srv import Empty, EmptyResponse # you import the service message python classes generated from Empty.srv.

def my_callback(request):
    print "My_callback has been called"
    return EmptyResponse() # the service Response class, in this case EmptyResponse
    #return MyServiceResponse(len(request.words.split())) 

my_service = rospy.Service('/my_service', Empty , my_callback) # create the Service called my_service with the defined callback
rospy.spin() # maintain the service open.

Every service callback gets that keyword, request, where you can access the parameters passed when the service was called.

In the case, we didn’t pass any parameters, so that’s why it was not used (but it still needs to be there).

You should find other examples where request was used.