Simple definition of Agile is given below along with the key terms highlighted. Take a look-
Time-boxed means all the activities/iterations/ceremonies are time bound. There is no endless, limitless time approach. At the end of that defined time limit, desired output should come.
Iterative model is a successive upgrade for a project. For example if we have to make a greeting card, we shall first create frame, draw the figures, then colour it and then decorate and complete it.
Incremental is piece wise delivery. With the same example, if we are making a card incrementally, we shall create one part of card completely and then increment it with next small part and it will go on till the completion stage.
How important is this feature to a Customer? Or How badly is this feature needed or not needed by a customer defines the Business Value of the feature.
Agile is a combination of all these. Where by following time-boxing, we incrementally iterate and release potentially shippable product after every iteration. This potentially shippable product is the one driven by business value as the features in it are prioritized by Customer as per their requirement.
Focus on Business Value is a core aspect of Agile. At the end of iteration, the amount of work is achieved with a quantum of value delivered. Potentially Shippable Product with a business value delivered with it in each increment is of foremost importance in an Agile based environment.