The phrase "double celebration" means a joyful event that is celebrated twice, either on two different occasions or in a repeated manner. It could refer to an event that is celebrated with great enthusiasm and happiness, such as a wedding or birthday party. The phrase can also be used to describe a situation where something that was previously celebrated is being done again, such as a promotion at work or winning an award. In essence, the phrase "double celebration" conveys a sense of joy and happiness that is experienced twice or in a repeated manner.