For those who dont know: PostgreSQL, often simply "Postgres", is an object-relational database management system (ORDBMS) with an emphasis on extensibility and standards-compliance. As a database server, its primary function is to store data, securely and supporting best practices, and retrieve it later, as requested by other software applications, be it those on the same computer or those running on another computer across a network (including the Internet). It can handle workloads ranging from small single-machine applications to large Internet-facing applications with many concurrent users. Recent versions also provide replication of the database itself for security and scalability. Check http://en.wikipedia.org/wiki/PostgreSQL JSON
JSON has existed for a while in Postgres. Though the JSON simply validates that your text is valid JSON, which can be really appealing at the very first moment, but really really frustrating when you have a huge collection and some of the documents contains bad values or there are missing some fields.
So to avoid this, begining with PostgreSQL 9.3 there are great features which can turn it into a NoSQL database, with full transaction support, and regarding to this article, with the ability to store JSON documents with constraints on the fields data, even defined operators for the JSON type, which give you easy access to the fields and values.