In my opinion ‘Inbound’ is a whole philosophy for business, encompassing the entire customer lifecycle as can be represented by the flywheel model, whereas ‘Inbound Marketing’ is the specific part of that philosophy focussed on lead generation and opportunity creation.
Inbound Marketing is supported by Inbound Sales and Inbound Service philosophies to help businesses provide a more customer-centric experience across their entire journey with the company.
What’s interesting is that while Inbound Marketing is predominantly geared towards generating new opportunities/customers though marketing communications, the flywheel approach aims to turn existing customers into a major source of new ones by improving success, satisfaction, loyalty and evangelism though good sales and customer service experiences.
Hope this helps.