What Are Loglines In Screenwriting

Hello friends, this is a small topic regarding Log lines in screenwriting, "Log line is nothing but summarizing all the concept of a film in maximum three to four lines revealing the main theme and the interesting sub plots in a film which will hook the viewer to think about the story"are known as log lines.
The main use of this log line is "advertising". Log line generates curiosity in audience. Helps in easy campaigning of the film through ads,television etc., also views can connect to the content easily.
These log lines are used to be treated as  a separate form in old Hollywood days, but as the days passed..these log lines are created to easily access the screenplay's from Hollywood screenplay library..i.e they use to right the whole summary of the film in one r two lines on the back of the screenplay or on the top so that one could find the content of the film without unstacking them. 
An example for this concept of log line can be found in the video below:

Log line For The Above Video: "The legend came as a shepherd, The legend came as a merchant, The legend came as a Lawyer and now the legend came as a Police"
Credits: Wikipedia