A software development philosophy that encourages the team to release the solution in increments throughout the project instead of delivering the solution all in one release at the end of the project.
Software projects have traditionally taken a waterfall approach. The restrictive nature of waterfall prevents the projet team from getting early feedback from the customer on an actual solution.
Agile is meant to help project teams overcome the most common challenges of waterfall by allowing the project team to do early releases to their customers and getting regular feedback to adjust the development of the product/system.
RECOMMENDED READING: What is Agile?
As a business analyst, you may be expected to work with a project team that operates in accordance with one of the many agile methodologies. You must master the core business analysis capabilities, and learn how to adapt your skills to deliver in a waterfall environment, in an agile environment, and in the most common type of environment: hybrid-agile.