Public speaking is speaking
 to a group of people in a structured, deliberate  manner intended to 
inform, influence, or entertain the listeners. In public  speaking, as 
in any form of communication, there are five basic elements, often  
expressed as "who is saying what to whom utilizing  what medium with what effects?
"The purpose of public speaking can range from
 simply  transmitting information, to motivating people to act, to 
simply telling a story.  A good orator should be able to change the emotions of their listener, not just inform them.
 Public speaking is a process of speaking
 to a group of people in a structured, deliberate manner intended to 
inform, influence, or entertain the listeners. It is closely allied to 
"presenting", although the latter has more of a commercial advertisement
 connotation. Public speaking is commonly understood as a kind of 
face-to-face speaking between individuals and audience for the purpose 
of communication.
History
Public speaking is almost as ancient as speech itself. The  first known textbook
 on the subject was written over 2500 years ago, and the principles 
elaborated  within it were drawn from the practices and experience of 
orators in ancient  Greece.
These basic principles have undergone modification as societies and cultures have  changed, yet remained surprisingly uniform.
Training
Effective public speaking can be developed by joining a  club such Rostrum, Toastmasters International, Association of Speakers Clubs (ASC)  or International Training in  Communication
 (ISC) in which members are assigned exercises to improve  their 
speaking skills. Members learn by observation and practice, and hone  
their skills by listening to constructive suggestions followed by new 
public  speaking exercises.
Leadership
Effective leadership almost always requires 
the skill of  good public speaking, and this can often make up for a 
lack of other skills.  The ends to which this skill can be used vary 
greatly - Adolf  Hitler and Martin Luther King, Jr. were both able to  use oratory to have a significant impact on society - but in very different  directions.
General
The fear of public speaking is called glossophobia (or, informally, "stage fright"). It is believed to be the single  most common phobia — affecting as much as 75% of the population. Fear of oration is ranked even  above that of death.