Report entities, e.g. columns, text entities, etc., can be grouped together and referenced as one object. Such a group is called a Block. Blocks can be re-used on different reports. Internal blocks can be referenced only by the same type of reports. For example, internal log blocks can only be referenced by log reports.
For example, you may have a border and title block that will be used in many graph report forms. You could copy or redraw the entities on every graph you create. A better way would be to store these entities in an internal graph block and then reference the block on the graph reports.
This is a short video describing creating an internal block: http://communities.bentley.com/products/geotechnical1/m/mediagallery/269620.aspx.
Working With Blocks Part 1: Introduction https://communities.bentley.com/products/geotechnical1/w/wiki/12371.working-with-blocks-part-1-introduction.aspx
Working With Blocks Part Two: Drawing Library Blockshttps://communities.bentley.com/products/geotechnical1/w/wiki/12372.working-with-blocks-part-2-drawing-library-blocks.aspx
Working With Blocks Part 3: Internal Blocks https://communities.bentley.com/products/geotechnical1/w/wiki/12374.working-with-blocks-part-3-internal-blocks.aspx
Working With Blocks Part 4: Private Blocks https://communities.bentley.com/products/geotechnical1/w/wiki/12378.working-with-blocks-part-4-private-blocks.aspx