Now a days you can go for only B.Com Honours since all the University has accepted the syllabus of U G C. In plain B Com which is also know as General B Com, you need to pass and obtain 33-40% marks depending upon university but in Honours Course you need at leat 45% Marks in each subject and they Honours will be awarded to you. For Honours course you need to study Extra subject too and opt the subjects for your Honours Course.

The B.com degree in simple words means passed in pass class and B.Com honours means passed in second class as said in the best answer. However, there is no need to study extra subjects as far as the Mumbai University is concerned.