Higher dimensional proton decay operators.

phystudent.9

I am new in this group and yet to know the rules about posting doubts/
questions. So first of all if anybody helps me with the guidelines
(which may be some link) to be followed, I will appreciate that.

Second, my main question is: what is meant by higher dimensional
proton decay operator? I have seen this term in some titles of papers
and also in Wikipedia article on proton decay, but I have not found
any explanation about its meaning. I have not come across such terms
in my elementary quantum field theory course. In wiki article, qqql/
(Lambda)^2 is said to be a dimension-6 proton decay operator. I do not
understand how that is so. can anybody explain?