Some attributes of the exposed variables are arrays. This means they're a representation of a collection of objects. They all share the same attributes:

nametypedescription
any?booleanreturns true if the collection is not empty, returns false otherwise
empty?booleanreturns true if the collection is empty, returns false otherwise
firstobjectreturns the first object of the collection
lastobjectreturns the last object of the collection
sizenumberreturns the number of items of the collection

You can iterate through an array using the Liquid's for loop:

{% for course in courses.enrolled %}
  {{ course.name }}
{% endfor %}