Oracle allows a few different syntaxes for specifying where to find your database service. The one I've seen most commonly (in the few short years I've been developing software professionally) looks something like this:
I don't think this syntax has any particular name, but it is what Oracle generates in its TNS files if you use graphical tools to modify it. But Oracle also allows the following much more compact syntax, at least with tools like SQL*Plus and application divers:
This is known as Easy Connect, and I have read that it was introduced by Oracle 10g. That makes it around 10 years old. I'm not sure if this can be used in a TNS file, and as short and simple as it is, I don't see much need to put it in a TNS file. Which is the good thing about it in my opinion: you can just use it directly with your application instead of needing to maintain a TNS file.
However, from the work I've done and the clients I've worked with, its usage seems to be rather uncommon. The only reason I even know about it is because ESRI started recommending its usage for establishing connections in newer versions of ArcGIS. That leaves me wondering why it's uncommon, so is there some kind of downside to using Easy Connect that I'm missing?
(I'd appreciate if someone could add more tags. I couldn't think of/find any more that made sense.)