Help screen toolbar icon Read More
From Joomla! Documentation
Read More: This button inserts a 'Read more...' break in the Article. This shows as a red dotted line across the Article. If an Article has a 'Read more...' break, only the text before the break, called the Intro Text, will initially display, along with a 'Read more...' link. If the User clicks this link, either the entire Article or just the part after the 'Read more...' link is displayed. This depends on the setting of the 'Intro Text' parameters for the Article and in the Global Configuration. The 'Read more...' break allows you to save space on pages by just showing the Intro Text. Note that the 'Read more...' break only shows in the Front Page, Section, and Category Blog layouts. If you want to insert breaks for an Article shown in an Article Layout, use the Page Break button.