Remittances, usually understood as the money or goods that migrants send back to families and friends in origin countries, are often the most direct and well-known link between migration and development.
Remittances exceed official development aid but are private funds. Global estimates of financial transfers by migrants include transactions beyond what are commonly assumed to be remittances, as the statistical definition used for the collection of data on remittances is broader.
Also, such estimates do not cover informal transfers. Remittances can also be of a social nature, such as the ideas, behaviour, identities, social capital and knowledge that migrants acquire during their residence in another part of the country or abroad, that can be transferred to communities of origin.
Details of Migration and Remittance data at World Bank here