Short answer
HubSpot's KB: click rate is recipients who clicked a link out of those who received the email; click-through rate is those who clicked out of those who opened it. An open counts when images load or a link is clicked, which is why privacy features and bots affect opens and CTR.
1. The Analyze tab
Marketing email Analyze in my demo portal.

2. Which to use
- Comparing emails to different lists: click rate.
- Testing content for people who opened: CTR.