A Speaker is the person who will speak during a session of the program: conference, workshop, demonstration, etc. Speakers are added in the same way as other attendees.

See: Adding "People" to an event

An Attendee becomes strictly speaking a Speaker when you associate him to a session of the program?

See: How to attach speakers to sessions?

You also have the possibility to create files for your Speakers without giving them access to the platform or linking these files to any profile.

See: What is I don't have the email address of a speaker?