difference between callout and web service salesforce?

Apex callout enables you to tightly integrate your Apex code with an external service and also enable Apex to invoke external web services. The callout makes a call to an external web service or sends an HTTP request from Apex code, and then receives the response. This allows you to connect to 3rd party web services such as Google, Amazon, Facebook, and any other external web service.
REST and SOAP are the two web service frameworks available on the Force.com platform. The SOAP API uses authentication with username and password and communicates using XML messages. There are different APIs to work with the Enterprise, Partner, Bulk, Metadata, etc.

Callout and Web service Salesforce are two different types of Salesforce Configurations. Callout requires a physical server and web service does not require a physical server. Web service is a completely web based configuration which means there is nothing to install on your PC. Web service is also cheaper as there is no need for hardware. Callout is a more secure configuration than web service as there is physical hardware & software which resides at a central location. Callout is generally used when the company is large and has its central services in one location. Callout is used when the company requires high security, large storage space and the ability to handle heavy loads. Consult the top experts to know clearly about how both these services work. To get the list of top salesforce consultants, visit here.