An electric car is a type of car that runs on electricity. Because it runs on electricity it is a zero emission car, a car that doesn't produce pollution at the point of use. It is probable that some type of fossil fuel would have been used to generate the electricity in the first place, in some cases all the electric car really does is move the pollution somewhere else.
Hype vs. Facts
Zero emissions sounds wonderful but it's not entirely true. While electric cars typically emit less CO₂, over its lifetime a Tesla S will emit about 13 tonnes of CO₂. The production of its batteries alone will emit 14 tonnes. 
Coal power still accounts for 39% of America's electricity power. This means that electric vehicles will still be responsible for producing CO₂. A North Carolina State University study showed that a nation full of electric cars powered will make no ecological difference.  This is due in part to its production costs, rare metal mining, energy consumed over its lifetime.
The battery is the heart of electric cars. Disposal of batteries is also a concern. Dead ones can't be tossed in a landfill and few companies will recycle lithium batteries and electric cars have many large batteries. Seasonal weather changes, extreme cold, affect battery performance. In 2014, it was measured to be half as efficient. 
- Don't be fooled - Elon Musk's electric cars aren't about to save the planet, The Telegraphe, April 6, 2016
- Tesla, The Coal-Powered Car, Won’t Be Saving The World, Investors.com, April 4, 2016
- The Cold Truth: Icy Temps Can Slash An Electric Car's Range By More Than Half, Forbes, March 24, 2014