Chartering in agile projects has the same general goal, but a different level of detail and set of assumptions. The goal of a Charter is still to describe the project at a high level, gain agreement into the W5+ (What, Why, Who, When, Where and How) attributes of the project and give authority to proceed. However, since agile methods are often used on projects with uncertainty around requirements / technology, and high rates of change, there is typically less certainty around scope.
In general agile charters have less detail, are shorter documents, and focus more on how the project will be run than what exactly will be built. This is because when aiming at a static target (unchanging requirements / technology) it is appropriate to plan, plan some more and then execute. In the dynamic and moving target environment of an agile project lots and lots of planning may not be appropriate if elements of the project are likely to change. So, when aiming at a moving target, we need to allow for mid flight adjustments and ensure the processes (prioritization, demos, retrospectives, etc) are in place to allow for them.
Elements of agile that may be different for an organization, for instance, welcoming changes and then prioritization of approved changes into the backlog, should be clearly outlines in the charter. This is especially important if the organization is new to agile and this may be a departure from how changes were handled in the past...