Greenwashing is what a company does when it makes a good or service seem more environmentally friendly than it really is.
Greenwashing can take a lot of different forms. A company may use words like "green" or "natural" to imply that their products and practices are sustainable, even if they're really not. An oil company may advertise its plans to protect endangered species and lower emissions, all while actually working to produce and sell more and more fossil fuels. In general, if a business spends more money on advertisements or other messaging that makes them seem environmentally friendly than on actually reducing their harmful environmental impact, they are practicing greenwashing.