You may hear that "VSTS is an ALM tool" when talking with a Microsoft rep or techie. This is not a misrepresentation but what they often mean is that "VSTS is an SDLC tool". Unfortunately marketing got their hands on this acronym and IMHO got it all tangled up. Lets deconfuse the two very distinct things:
SDLC == Software Development Life Cycle; this includes everything to do with DEVELOPING a software application, including requirements, architecture, coding, testing, configuration management project management
ALM == Application Life Cycle Management; as the name suggests includes everything that is part of the Application Lifecycle. When does the life of an apps start? No, not in development, it starts somewhere in the business as an idea, a need, a challenge, a risk. When does the life of an application end? No, not at the end of development, but when the application is no longer used by the business - potentially many years after the initial development.
I use the following slide to deconfuse confused folks:
These days the SDLC is typically iterative in nature, but so is the Application life Cycle! As the business responds to an ever changing environment, we start yet another ALM cycle to update, enhance the application and redeploy so the business can realise the benefits.
It's really that simple.