The Loss Tangent:
The loss tangent is a parameter that characterizes the lossiness of a dielectric material. It is defined as the ratio of the imaginary part of the complex permittivity to the real part of the complex permittivity. Mathematically, it is represented as:

Loss Tangent (tan δ) = Imaginary part of permittivity (ε") / Real part of permittivity (ε')

Lossless Dielectric:
A lossless dielectric is a material that does not dissipate any energy when subjected to an alternating electric field. In other words, it has zero electrical conductivity and no energy losses. This means that the real part of the complex permittivity is much larger than the imaginary part, resulting in a very low loss tangent (tan δ ≈ 0).

Explanation:
When the loss tangent is very less (close to zero), it indicates that the imaginary part of the permittivity is much smaller compared to the real part. This implies that the dielectric material has very low energy losses when subjected to an alternating electric field. Such a material is known as a lossless dielectric.

A lossless dielectric is an excellent insulator and can store and transmit electrical energy without significant losses. It is commonly used in applications where high insulation properties are required, such as in capacitors, transmission lines, and dielectric substrates.

Comparison with Other Options:
- Conductor (option A): A conductor has a high electrical conductivity and exhibits significant energy losses when subjected to an alternating electric field. The loss tangent of a conductor is relatively high (tan δ > 0).
- Lossy Dielectric (option C): A lossy dielectric has a higher loss tangent compared to a lossless dielectric. It exhibits moderate energy losses when subjected to an alternating electric field.
- Insulator (option D): Insulator is a broad term that includes both lossless and lossy dielectrics. However, in this specific context, the correct option is B, which refers to a lossless dielectric.

Conclusion:
In summary, when the loss tangent is very less, it indicates that the material is a lossless dielectric. A lossless dielectric has low energy losses and is commonly used as an insulating material in various electrical and electronic applications.