Salesforce CTI enables Salesforce to be used as a call center. The technology plugs your telephony into Salesforce, allowing for softphones to be deployed right inside your CRM instance for each of your call center agents or inside sales teams (or both of course).
An inbound call center is set up to primarily receive communications initiated by customers and prospects. Most inbound call centers are therefore customer service focused, as it is people calling in when they need assistance with a product or service.
An outbound call center is set up to primarily initiate communications and phone calls to customers and prospects. Most outbound call centers are therefore sales focused, making calls to customers and prospects to try and make a sale.
This may seem like common sense, but it really does come down to the primary direction of the vast majority of your activity in your call center. If over 50 percent of your calls are inbound, then you are an inbound call center.
This distinction is an important one to make as it will shape what you need from technology and what types of processes and protocols you should implement. For example, an inbound call center is unlikely to need advanced dialer capability.