- Call-To-Action
- Campaign
- CAN-SPAM
- Canonical URL
- Categories
- Category
- Channel
- Chat
- Cloaking
- CMS or Platform
- Comments
- Confirmed Opt-In (Double Opt-In)
- Conversion
- Conversion Form
- Conversion Rate
- Conversion Rate Optimization (CRO)
- Cookie
- Cost Per Click (CPC)
- Cost Per Lead (CPL)
- CPM (Cost per Thousand)
- Crawler
- Creative Commons
- CRM
- Cross-Channel Analytics
- Crowdsourcing
- CSS or Stylesheet
- CTR (Click Through Rate)
- Customer Lifetime Value (CLTV)
- Customer/Buying Lifecycle