The correct answer is option 'D', an aquitard. An aquitard is a geological formation that contains water but has a very low permeability, meaning it yields only an insignificant quantity of groundwater. Let's explore this concept in more detail:

1. Definition of an Aquitard:
- An aquitard is a geological formation that restricts the flow of groundwater due to its low permeability.
- It can be composed of clay, silt, or other fine-grained materials that do not allow water to pass through easily.

2. Characteristics of an Aquitard:
- An aquitard has a low hydraulic conductivity, which means it has a low ability to transmit water.
- It acts as a barrier or confining layer between aquifers, preventing the easy movement of groundwater.
- While it may contain water, the quantity of groundwater it yields is insignificant due to its low permeability.

3. Comparison with Other Terms:
- Aquifer (option 'A'): An aquifer is a geological formation that can store and transmit significant quantities of groundwater. It has high permeability and can be a source of water for wells.
- Aquifuse (option 'B'): Aquifuse is not a recognized term in hydrogeology and does not pertain to groundwater formations.
- Aquiclude (option 'C'): An aquiclude is a geological formation that completely blocks the movement of groundwater due to its impermeability.

4. Examples of Aquitards:
- Clay layers: Fine-grained clay deposits can act as aquitards due to their low permeability.
- Shale formations: Shale, a type of sedimentary rock, can also serve as an aquitard.
- Unconsolidated silt: Loose, fine-grained silt can restrict the movement of groundwater.

In summary, an aquitard is a geological formation that has low permeability, resulting in an insignificant yield of groundwater. It acts as a barrier or confining layer between aquifers, restricting the flow of water. Clay, shale, and unconsolidated silt are common examples of aquitards.