Plastic as a term refers to a series of short (or sometimes semi-synthetic) materials, usually solid, especially in industrial applications. In general, polymers (ie large chains of molecules) with a high molecular weight, sometimes, other substances are introduced to reduce the cost of production.
The use of plastic in its name says: Plastic comes from the Greek "plastikos" which means "capable of being molded." This capability means that the plastic can be turned into an almost infinite variety of forms, regardless of size, and yet, it will harden and become firm and lasting. Some useful forms including fibers and films, plates, tubes, bottles and boxes, and many more.
Due to the relatively low cost involved, and the ease of which can be manufactured, plastics are used in a wide variety of products. They are versatile and durable, and therefore, have replaced many traditional building materials such as leather, wood, stone, bone, metal, ceramics and glass.
There are two main types of plastics: thermoplastics and thermosets. Thermoplastics do not undergo a change when heated, so it can be molded over and over again once it reaches the temperature (hence the name prefix thermo). Solid thermosets stay permanently once you have set (hence the value), but, obviously, can be melted again, but can not be reformed.
Alexander Parkes, a British engineer, invented the first artificial plastic in the mid-nineteenth century. Parkesine appoint the material, Parkes showed that his creation could be heated, molded and cooled, retaining its shape once it set. Parkesine was far from the plastics that we know today, was very flammable, expensive and prone to cracking. Plastics developed in the rest of the century, though not particularly a material widely used until the middle of next century.
Plastics are durable, but they degrade very slowly. Molecular bonds that make plastics so durable are the reason for its durability. Billions of tons of plastic have been dumped since the mid-twentieth century, much of which still exist in many thousands of years. The production of plastics can create chemical pollutants, and burning of plastics often produce noxious fumes which are often poisonous. However, recyclable plastics are widely, especially in more developed countries where there have been mass produced, meaning that plastics can be used more widely and more ethically than ever.