The previously mentioned Office 365 suites are a collection of online services that, when purchased together, give customers what we call a suite discount. Customers who do not need or want to buy full suites can purchase individual services as separate products. Note that some of these online services have technical dependencies on others. For example, Exchange Online Protection (EOP) provides an added level of security to the Exchange Online and/or Exchange server services; customers can't use EOP if they don't have either Exchange Online or Exchange server deployed.
For more information on the technical dependencies, refer to https://technet.microsoft.com/en-us/library/office-365-service-descriptions.aspx.