When you look at the evolution of NoSQL it has primary evolved to solve specific problems that were difficult, not impossible, to solve using a traditional RDBMS. In other words, NoSQL became perhaps a "better" or "different" way to solve a problem. A lot of NoSQL solutions achieve their scalability by choosing to make compromises on things like consistency and transactions.
But what if you didn't want to compromise? What if you wanted scalability and things like ACID compliant transactions? Well a new crop of database startups started to emerge. Solutions like VoltDB, Clustrix and ScaleDB. Essentially they were a hybrid database offering a traditional RDBMS that could scale. Well now that group of databases have a new name, NewSQL!
The 451Group published a blog post in which they described what the term meant along with the players they felt fit within the group. Here's what the had to say about the term:
“NewSQL” is our shorthand for the various new scalable/high performance SQL database vendors. We have previously referred to these products as ‘ScalableSQL’ to differentiate them from the incumbent relational database products. Since this implies horizontal scalability, which is not necessarily a feature of all the products, we adopted the term ‘NewSQL’ in the new report.
The reaction so far by many of the companies included in the group has been extremely positive. In the end it's just a name, a way to categorize a group of similar solutions. It does bring a sense of legitimacy to the product group, as well as, a name to rally around as these solutions grow. And so the NewSQL era begins!