Is Opportunity associated with an Account or an individual Lead?

Is Opportunity associated with an Account or an individual Lead?

I'm bit confused with the term Opportunity and need following clarifications based on your use-cases:

Is Opportunity associated with an Account or an individual Lead?: As I understand, during lead's journey in Marketing-automation funnel, a lead is tracked individually. In the sales-funnel, salesperson attaches any potential revenue/opportunity note with this lead and converts it to a Contact. Finally, multiple contacts get associated with an account and an opportunity amount is added at Account level. Plz correct me, if I'm wrong?
 
So, when we talk about term Opportunity, do we refer to a deal for a lead or an account? 

Thanks & regards,
Rakesh Pathak 
Product Manager | Zapstitch