Direct Plan and Regular Plan of Mutual Fund are most likely not a new term for people if you are not living under rocks from last few years.
Certainly, there are many articles pop-up when you do simple Google search. In simplistic words, when you buy funds under Regular Plan you have a distributor in-between you and AMC (Asset Management Company), who get a small portion (roughly about 0.30% to 0.80% on average) of your every investment from AMC on your behalf as part of the expense ratio. Wherein, when you go with Direct Plan then you are directly dealing with AMC so no such charge being paid hence their expense ratio is low compared to Regular Plan. But as Uncle Ben said in Spiderman, With great power comes great responsibility. By saving a small percentage on Direct Plan we loose helping hand too, as most of Financial Advisor act as a distributor to provide discounted advice services.