A namespace is an abstract container or environment created 
to hold a logical grouping of unique identifiers (i.e., 
names). 
Namespaces allow to group entities like classes, objects 
and functions under a name.

namespace is a one of the problems solved by namespaces, 
that of conflicting class names

it is used to solve the problem when there is conflict 
between class names

namespace is used to avoid class name collision.

Namespace is logical group of classes.It can span multiple 
assembly.

Namespace is a group of classes, structures, interfaces, 
enumerations, and delegates, organized in a logical 
hierarchy by function, that enable you to access the core 
functionality you need in your applications. 
Namespaces are the way that .NET avoids name clashes 
between classes. A namespace is no more than a grouping of 
data types, but it has the effect that the names of all 
data types within a namespace automatically get prefixed 
with the name of the namespace. It is also possible to nest 
namespaces within each other.