Which type of variable can store multiple values in Appian?

The type of variable that can store multiple values in Appian is the multi-value variable. Multi-value variables allow developers to represent a list or an array of values within a single variable. This is especially useful when dealing with situations where a set of data is required, such as lists of users, orders, or any collection of items.

In Appian, single-value variables are designed to hold only one value at a time, which limits their use when multiple entries are needed. Document variables, on the other hand, are specifically for storing documents and are not applicable for general multiple values of data types. Lastly, process variables focus on storing data specific to the execution of a process instance and are not inherently designed to hold lists of values by themselves.

Thus, the multi-value variable stands out as the correct choice for storing multiple values due to its defined capability to handle arrays or lists efficiently in Appian applications.