The material that hinders the passage of the electric current. In this type of material, the electrons in orderly flow their movement is impeded. Note that the definition of dielectric is exactly the same for electrical insulator. These two terms are synonymous, so we can define dielectric as being an insulator of electricity.
Dielectrics fulfill the important function of protect an individual from direct contact with a potential energized conductor, therefore, they are used as personal protective equipment (PPE) in various activities. Another function of these materials is the composition of structures of capacitors, allowing a closer approximation of the plates that make up the device. As examples of dielectric materials, we can mention the dry wood, pure water, glass, plastic, rubber, ceramics, air etc.
Breaking dielectric strength
When a dielectric is subjected to a electric potential difference big enough, it can be ionized and start to behave like a conductor. When the insulator is momentarily forced to conduct electricity, we say that its dielectric strength has been broken.
The electrical discharges we call lightning or lightning they occur through the breakdown of the dielectric strength of the air.
By Joab Silas
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/fisica/o-que-e-um-dieletrico.htm