A domain is a terminology of software engineering. A domain is the aimed study region of a software application. There are two types of project domains.
Application specific Project Domain
Programming Language specific Project Domain.
For example, finding a credit card fraud is a application specific project domain. It can be machine language domain or deep learning domain depends on which algorithm is implemented to predict credit card fraud. For example, if SVM or Random Forest is implemented to predict, then it is called as machine learning domain. If it is implemented using any neural network algorithm, then it is called as deep learning domain.