What is a custom data type?

Custom data type is a data type used on a step property.  A given step may have many # of inputs, each input is rendered using a data type.  For example, if you look at the inputs for the "Decision" step:

The decision step has an input called "Condition to evaluate", this input is rendered using the "multilineTextBox" data type.  So, each input must have a data type, by default most inputs use the "string" data type which renders as a text box.

See the full Step by Step guide HERE.