What is the difference between respondents and campaign members?

Campaign member

A campaign member is the recipient data added to a campaign. Each campaign member will be added with an unique ID.
A campaign member can appear on all tabs in the campaign member table; Responses, Delivered, Scheduled, and Failed.

Respondent

A respondent is the data you see under the respondent tab. A respondent will be added, the first time a recipient is added to a campaign and will appear on the campaign as a campaign member.

A respondent can belong to several campaigns as a campaign member. This means, that if you delete a respondent, you will also delete all related campaign members.