Like dean said, huge buzz word is what CRM is. Just a set of methods, whatever medium they might be in, to manage a potentially huge list of existing customers while inviting new ones.

Your biggest customer is the customer you already have, you want to maintain that relationship with them as best as possible. To do so effeciently with a mass number of customers already in line you need a method of managing it effectively.

Also, with CRM you can generate reports for analyzation of what kind of customers you are generating revenue from, etc.