What is flow? Flow is a (cloud) engine for workflow automation, which is developed and provided by Microsoft.
With this engine, recurrent processes or data distribution tasks can be efficiently handled.
These recurring processes can be a daily reminder email or the creation of customers in D365 for Finance and operations you previously created in CRM online. Also quotes from CRM can be transfer to D365 Fin/Ops transferred or suppliers can be created from an Excel file.
Flow is seamlessly integrated into the online world of Microsoft products. It also offers to many other tools that do not directly belong to the Microsoft world, the possibility to interact, for example data can be written using flow from Twitter into a SQL database, follows by analyze Power BI (a Microsoft product) to evaluate these and all of this is done in Azure, which it worldwide and everywhere and for everyone available. As more services, Facebook are here to mention also then dropbox and many others. (continuous rise since October 2016 by 53 services to over 150 services in August 2017)
The best thing is that Flow is fully usable without knowledge of program code, the end user get the availability to define workflows from simple to highly complex.
Hereby I woke your interest? Then quickly go to flow.microsoft.com and try it out yourself. But be careful, there is a risk of addiction.
Would be happy to hear of your results or ideas
This is no official descricption from Microsoft. It´s only my experience and thinking.