What is the difference between a validation and a development set? For most of the ML problems we have train,test and validation sets in a dataset as discussed in this thread. I have a dataset where I have train, development and evaluation sets. train and evaluation sets are obviously train and test sets. What about development set? Is it the same remaining validation set or it has a different concept?

Yes, it is the validation set. Related wiki entry:

A validation dataset is a dataset of examples used to tune the hyperparameters (i.e. the architecture) of a classifier. It is sometimes also called the development set or the "dev set"

