Green Monday is an online retail industry term similar to Cyber Monday. The term was coined by eBay to describe its best sales day in December^[1], traditionally the 2nd Monday of December. Green Monday is defined more specifically by business research organization comScore as the Monday with at least 10 days prior to Christmas. In 2009, $854 million was spent online in the US on Green Monday,^[2] with sales in 2011 reaching $1.133 billion. ^[3]Green Monday in Greece and Cyprus is the movable feast day known elsewhere in the Greek Orthodox Church as Clean Monday, the first day of Lent - approximately seven weeks before Easter. Traditionally families go to fields to barbecue fasting foods such as vegetables and seafood (not meat), later flying kites and playing other games.

Green Monday also refers to a network of sustainable development practitioners in the UK, which meets on the first Monday of every month in London to discuss critical environmental issues affecting business and industry. Climate change is a major theme.^[4]