When learning these terms, it might be helpful to think of this analogy:
"Entities" are like actors.
"Prospects" are like roles an actor considers throughout his career - they won't play every role offered, but will consider taking part.
"Proposals" are scripts an actor reviews, and then accepts or rejects, or perhaps negotiates for better terms.
"Programs" are projects directors might have in mind for an actor, based on the roles the actor has played in the past.
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