Note: I took this post from another forum where I answered the same question.
Simply put, ERP software (ERP standing for Enterprise Resource Planning) is a fully integrated system that includes inventory, accounting, order entry, purchasing and contact management. ERP software is designed as an end-to-end solution for all aspects of business operations. Some ERP systems will have eCommerce integration and industry specific functions (such as additional features specific to those in the catering industry). Essentially ERP software is one system that replaces the need for integrating multiple software systems across departments. I work for an ERP company called Blue Link Associates that does all of the above and we come across a lot of people unfamiliar with the term so it is nice to be able to break it down into its simplest form - hopefully this helps!
You can learn more here: http://blog.bluelinkerp.com/2011/08/25/what-is-erp-software/
ERP is Enterprise Resource Planning. Think of it like accounting software on steroids.
Accounting software handles only individual business financial functions but Enterprise Resource Planning (ERP) software does the entire range of business functions for a company.
For example HR, Production, Distribution, Manufacturing, Field Service etc...