In agile development you focus on smaller cycles of development as opposed to the more structured style (waterfall) of coming up with a full design document -> code to completion -> test -> release.
The buzzword that gets thrown around is a popular form of agile which is known as scrum where you have quick daily stand ups 2-3 week development cycles known as sprints etc.
This sounds all good on paper but what happens is that when a project is miss managed and won't deliver on time the business side freaks out and causes the project to release half finished or gets pushed back.
So how can this happen? Well for starters when the business comes up with a plan (known as stakeholders) they create a list of items that the project needs to do which are called stories. When I worked at a top 5 company they wouldn't have developers in these meetings and would set a time goal that they think that the project should delivered in a set time that is usually too short.
The second problem is that these stories are usually not written properly and many times one story is really five.
Third problem is that stories sometimes have to go in a specific order meaning that you can't design a feature for something that hasn't been created because as with the second problem of stories not being written well there might need to be a change.
Fourth problem is when your q&a department doesn't know how to test the code you wrote because of the second and third problem listed above.
Fifth problem is the time it takes for the stake holders to notified of these problems which slows down the development and Q&A from testing which results in stories not finished in the current sprint and get pushed back.
This doesn't mean I am against agile development. When it is done right it can be a thing of beauty but the problem is that software development is 90% bullshit and 10% actual development.
The main take away here is that there is no one right way of handling things in development. I hope this gives you an inside look as to what happens in enterprise level development.