External and Internal Communication :

When
the members or workers of different organisations communicate with each other,
it is called as External Communication.  That is, the members or workers
of the organisation communicate with the outside party. External communication
is mostly formal.  Its purpose is to maintain relationship  with
another institution or organisation. customers, shareholders, investors,
clients, etc. are the participants of External Communication. It has low
frequency.

When
the members of the same organisation communicate with each other, it is called
Internal Communication. It flows within the same organisation. It takes place
among and between managers, heads, supervisors and workers working in the
different departments in the same organisation. It is both formal and informal.
Its frequency is very high.