CRM = Customer Relationship Management is the management of the entire customer interaction the company has with its customers.   It’s a business strategy that helps you to better understand your customer, retain customers, provide excellent customer service, win new clients and increase profitably.  CRM relies heavily on technology

ERP =  Enterprise Resource Planning. ERP software is used to manage the business. It integrates all facets of an operation, including product planning, development, manufacturing processes, human resources, financials and sales and marketing.

CRM is typically used to manage the front end of the website, including marketing programs, customer interactions, etc.
ERP is used to help run the back end of the business.   Merging the two systems to efficiently manage the business with effective data management is a key factor in business success.