The phrase immediate application is the criterion, so the answer must be the type of research whose findings are put to use straight away in the situation that prompted it.

Action research is that type. It is undertaken by practitioners - a teacher, a principal, an administrator - to solve a specific problem in their own immediate setting. A teacher troubled by poor performance in a particular topic might try a new method with the class, observe the result, and modify practice accordingly. The cycle is plan, act, observe, reflect, and then plan again. The findings are applied at once, by the person who conducted the study, in the very situation studied.

Its scope is deliberately local. It does not aim at generalisation to other classrooms or at contributing to general theory, and its results may not transfer elsewhere. That limitation is the price of its immediacy, and it is why action research is classified separately from the research streams that seek wider validity.

Fundamental research, also called basic or pure research, is the opposite. It aims at discovering general principles and extending knowledge for its own sake, with no immediate practical use in view; applications may follow decades later or not at all.

Conceptual research works with ideas, definitions and theory rather than with observation or experiment. It develops or reinterprets concepts, which is again theoretical rather than immediately applicable.

Empirical research is defined by its method rather than by its purpose - it relies on observed and measured data. Much empirical research is applied, but much is fundamental, so the term does not by itself signify immediate application. This makes it the main distractor for a candidate reading the options loosely.

Hence the research stream of immediate application is action research.