"Agile" is, as best as I have been able to tell, defined as "anything not waterfall."<p>The line "The IT industry today treats waterfall as something old while agile is cool" reflects more the lack of general understanding people have of software engineering and history.<p>"Not waterfall" was as a common theme in the famous 1969 NATO conference which kicked off 'software engineering'. For example, (quoting <a href="http://homepages.cs.ncl.ac.uk/brian.randell/NATO/nato1968.PDF" rel="nofollow">http://homepages.cs.ncl.ac.uk/brian.randell/NATO/nato1968.PD...</a> ):<p>> The need for feedback was stressed many times. ...<p>> Fraser: (from The nature of progress in software production) »Design and implementation proceeded in a number of stages. Each stage was typified by a period of intellectual activity followed by a period of program reconstruction. Each stage produced a useable product and the period between the end of one stage and the start of the next provided the operational experience upon which the next design was based. In general the products of successive stages approached the final design requirement; each stage included more facilities than the last. On three occasions major design changes were made but for the most part the changes were localised and could be described as ‘tuning’. ...<p>> The use of feedback from a partly designed system to help in design, was discussed at length.<p>Of course, "waterfall" as a development model wasn't even formally described until a year later, or coined for another 7 or so years.<p>I like the description from <a href="http://tomasp.net/blog/2019/software-engineering/" rel="nofollow">http://tomasp.net/blog/2019/software-engineering/</a> that:<p>> For waterfall, the context was a more general managerial culture of the 1970s, rising complexity and costs of software, and the fact that programmers were "hackers" who were hard to hire, train and replace.<p>That is, while 'iterative but speedy design to delivery' is old - has been around since the 1960s - its coolness now comes as a reaction to a certain managerial style from the 1970s, which was a reaction to early agile.<p>Many of the concepts in agile, like rapid prototyping, were well-known in the 1980s and 1990s, and by the mid-1990s - well before 'agile' was coined - considered best practices.