Why is an electron negatively charged, and what is the difference between negative and positive charges?

Nobody has yet defined the actual meaning of a charge, or why a negative charge is different from a positive charge.

1. 
   
   

   Everybody knows that positive charge is due to protons and negative charge is due to electrons, but what does the charge mean?

   
   


2. 
   

   Why were negative and positive charges so designated?

   
   


3. 
   

   Was it also a possibility to call the charge of an electron positive and the charge of a proton negative?