Namespace Definition:

A namespace refers to a specialised section, which is used to define the scope of identifiers used in a programming language like C++. Identifiers can be anything: functions, variables, and etc. Namespaces help in organising codes into their respective logical groups and preventing name collisions within C++. 

All identifiers are arranged in such a way that each of them can see one another without any specific qualification. 

When you are using only one to two identifiers, you should use the declaration to let identifiers come within its scope while keeping other identifiers outside the namespace. A using directive should be positioned at the header of a .CPP file. You must not use directive in header files in usual cases because it will then include all elements in the namespace—it may lead to name collision, which is extremely tough to debug. 

Define Namespace Member:

Namespace members can be defined using a lot of blocks in either a single file or multiple folders. A compiler helps in joining parts of namespaces through processing, with all members constituting the namespace. 

The global namespace 

When an identifier is not clearly mentioned in an explicit namespace, it automatically becomes part of the implicit global namespace. Programmers are advised not to make declarations at the global namespace as far as possible. 

The Standard Namespace

The standard namespace or std namespace refers to standard library types and functions in C++. 

Namespace Aliases

Namespace Aliases can be used to denote a name using codes only. When names become too difficult to read or are too long, programmers use namespace aliases to simplify the task.