You'll probably get a few different answers on this.
The way we explain it to customers is that configuration is point and click - so things like custom fields, workflow, page layouts, record types, formula fields etc. Customization, on the other hand, requires code to be written so that covers Apex and Visualforce. Where possible you want to do things via configuration, as it means a lower skill set is required to maintain, you don't need to retest when a new platform release comes along etc.
Configuration is basically the administration part which includes things like - custom objects's fields, user management, permission sets, profiles, roles etc etc basically which can be done using point and click. Customization includes things like creating own custom objects, apex classes, visualforce pages, triggers, custom UI using jQuery plugins, writing custom css etc etc basically the work that developer has to do and takes most of the time :)
You'll probably get a few different answers on this.
The way we explain it to customers is that configuration is point and click - so things like custom fields, workflow, page layouts, record types, formula fields etc. Customization, on the other hand, requires code to be written so that covers Apex and Visualforce. Where possible you want to do things via configuration, as it means a lower skill set is required to maintain, you don't need to retest when a new platform release comes along etc.
Customization includes things like creating own custom objects, apex classes, visualforce pages, triggers, custom UI using jQuery plugins, writing custom css etc etc basically the work that developer has to do and takes most of the time :)