Continuity
A hookup does not necessarily imply future contact. FWB usually describes a recurring relationship.
Friendship
Friendship is central to FWB. A hookup can happen between strangers, acquaintances, dates or friends.
Expectations
FWB often benefits from explicit conversations about the ongoing arrangement because there is more relationship continuity to manage.
Neither label defines consent or exclusivity
Whether protection is used, whether either person has other partners, and what activities are comfortable still need direct communication.
Labels describe; agreements define
FWB, hookup, casual dating and situationship are useful shorthand, but none of them automatically answers whether a relationship is exclusive, how often people communicate, whether sex is involved, or whether either person wants commitment later. Two people can use the same label and still have materially different expectations. Treat the label as the beginning of the definition rather than the complete definition.
Choose the comparison that changes a decision
Relationship labels are most useful when the distinction affects what you do next. If the question is whether to date other people, discuss exclusivity. If the question is whether this is becoming romantic, discuss intention and expectations. If the question is sexual health, discuss partners, protection and testing. The practical issue should drive the conversation.
Labels help describe a relationship, but expectations are specific to the people in it. When something important changes, a direct conversation is usually more useful than trying to decode a rule from the internet.