A silent film is a film in which the sound track is not synchronised with the moving pictures. This specifically meant that speaking was impossible to reproduce, as it requires nearly perfect synchronisation between image and sound. Nearly all silent films were made before 1927, when technology finally made it possible to put the sound track directly onto the film through optical means; the first film to feature speech (and singing) was The Jazz Singer. Since the public wanted something to keep its ears busy while watching a silent movie, an orchestra would play some music during the showing, usually following some prewritten musical score. However, the later silent movies had an unsynchronised sound track instead of orchestral accompanyment — for example, the "charge of the cavalry" scene would be accompanied by the sound of horses galloping.
Since telling a story using only moving pictures is hard, most of the silents featured intertitles, or bits of text projected for a few seconds between two shots; they featured dialogues or details about the story. It may seem a weak way to express oneself, but it had its advantages. It made a movie very easy to export to foreign countries, as there were only the intertitles to modify. In Europe, making a movie for different countries with stars from each of them became so commonplace throughout the 1930s that films were shot simultaneously in various languages, with different actors but only a single director. It also prevented the confusion between the theater and the cinema, allowing the latter to develop as a independent art form. Making intertitles was an important part of the movie industry; in fact, both Alfred Hitchcock and Joseph Mankewicz started out in the business as intertitles writers. However, the skills of a director were measured by his ability to tell the story with as few intertitles as possible; F. W. Murnau achieved this in Der Letzte Man, which has only one.
Since most silent movies were made during the first three decades of the 20th century when color film wasn't available for cinema, those movies were shot in black and white. However, as a means of adding expressivity, in some movies each shot would be colored in a different color — for example, blue for night and yellow for the midday sun, as might be seen in Nosferatu.
For the modern viewer a silent film might seem strange, an obsolete form of art, one that can be forgotten. Yet it works very well for some kinds of films, such as the slapstick comedy. Charlie Chaplin and Buster Keaton made their best films without sound. Charlie Chaplin understood so well the advantages of not using sound that he continued to make silent movies for a while after the appearance of the talkies. And many masterpieces were made during the silent era; it would be a shame not to see them simply because they have no sound.
Some great directors of that time :
And I'm forgetting dozens of them.