I think you can find many different kinds of CRMs. At the core a CRM is for costumer relationship management, which means tool for optimizing your business client support. You have many tools such as: inbound call centers, clients tickets opening, share status with other departments and more.
Although, CRM has evolved over time and now contain features of marketing and in-office tools. You can find more information searching on google or getting to CRM websites such as salesforce
or MyBusiness CRM