Linkage describes how names can or can not refer to the same entity throughout the entire program or a single unit. Linkage is particularly useful in C++.
The static keyword is used in c to restrict the visibility of a function or variable to its translation unit. This is also valid in c++.
A name's linkage is related to, but distinct from, its scope. The scope of a name is the part of a translation unit where it is visible. For instance, a name with global scope (which is the same as file-scope in C and the same as the global namespace-scope in C++) is visible in any part of the file. Its scope will end at the end of the translation unit, whether or not that name has been given external or internal linkage.
If the name has external linkage, the entity that name denotes may be referred to from another translation unit using a distinct declaration for that same name, and from other scopes within the same translation unit using distinct declarations. Were the name given internal linkage, such a declaration would denote a distinct entity, although using the same name, but its entity could be referred to by distinct declarations within the same translation unit. A name that has no linkage at all cannot be referred to from declarations in different scopes, not even from within the same translation unit. Examples of such names are parameters of functions and local variables. The details differ between C (where only objects and functions - but not types have linkage) and C++ and between this simplified overview.
Static Linking
In static linking, the compiled functions are stored into the executable or dynamic library (if you're creating one).
Dynamic Linking
In dynamic linking, the compiled function is stored in a separated library (DLL in Windows or shared object in Linux). A small piece if code is added to the executable to load that shared library at runtime and map the public functions and variables within it.
