Primitive Obsession

Primitive Obsession is using primitive data types to represent domain ideas. For example, we use a String to represent a message, an Integer to represent an amount of money, or a Struct/Dictionary/Hash to represent a specific object.  

In fact, if we can create an object to represent the data type, not only the basic data but also more functional attributes can be created and managed.

For example, we need to create a message type with attributes 'title', 'body', 'sender', 'receiver', 'created_date', 'attachment', 'is_deleted' and so on.  You can realize at once that it's impossible ( or at least very difficult ) to use 'String' data type to represent all the attributes, including 'created_date'. The best way is to utilize object-oriented programming features: 'OBJECT'!  Just create a 'Message Object'.

There is a good article with better explainations:    
Get Rid of That Code Smell – Primitive Obsession