Constant Contact encourages the use of asynchronous background jobs to manage large collections of data. The Bulk Activity collection is used to create and manage those jobs, called Activities. Currently, the collection allows you to create jobs to add, remove and download contacts from contact lists. It also allows you to check the status of a customer's activities and to see when an activity is completed and whether it succeeded or failed. A single "call" to the "Activities" resource generally operates on a set of contacts. The data for that set of contacts is held in a formatted file, described in the link below.