Pubs and Bars are almost same terms with slight difference.Both are known for serving alcohol.
Firstly talking about Pub, In pubs people used to go for Drinking alcohol,Dancing and and food.More variety and type of food available in pub.Drink is optional in pub unlike bar.Pub is mailly for hangout and chill out for young crowd.Families are also allowed in Pubs.Office functions,farewell and other programmes can be organised in pubs.There are also entry fees in some pubs.
Now coming to bar,Bar is mainly for taking alcohol like beer,wine,etc.waiters used to serve alcohol there.We can enjoy alcohol and food there.Singers and dancers also performs at Bar.Families are generally don't like to go to bar.Even children are also not allowed.
So Pub is for overall enjoyment including food,dancing,etc and bar is for drinking purpose mainly.
Hopefully these are major differences....if you like to add something...Please put your views in comment section....