ERD is an Entity Relationship Diagram which is a graphical representation of database entities (tables, table columns, table definitions, attributes) and inter-relationships between these entities (how the tables are connected).
Here is simple ERD for the website with news section updated by users:
This simple ERD has 3 tables: users, news, and newsComments. It is easy to understand the attributes and data relationships.
Please note, this is a very simple diagram, most ERDs include 100s of tables. For example
Why it is important:
For the Website Owner - It is easiest way to describe relationships between data and to get a picture of functionality needed for the website. This reduces development time, helps meet deadlines and saves money.
For the Website Developer - It is easy to assess time to program, and accurately project deliverables, timelines and pricing.
Michael P.