Nest egg refers to a sum of money that has been saved up for a specific future use, such as retirement or emergency expenses. There are several synonyms for nest egg, including rainy day fund, contingency fund, emergency fund, and retirement savings. A rainy day fund is similar to a nest egg, as it is money set aside for unexpected expenses, while a contingency fund usually describes money kept aside for a particular purpose. Retirement savings can be considered a type of nest egg that is specifically reserved for one's later years. Whatever term is used, having a nest egg is a crucial aspect of personal financial planning and can provide peace of mind during uncertain times.