What's the difference between agile and waterfall?

The two main development methodologies are agile and waterfall. They are commonly applied to software development, and thus, project management as well. The main difference between agile and waterfall is that waterfall projects are completed sequentially whereas agile projects are completed iteratively in a cycle.
Both the agile and waterfall methodologies carry their own set of advantages and disadvantages. Overall, both can be beneficial to a software development team. Which one to choose is highly dependent on the project type and circumstances.