The ascribed difference is pretty straightforward:
- Match percentage indicates a statistical likelihood of reciprocal romantic interest between a given pair of users
- Friend percentage indicates a statistical likelihood of reciprocal friendship compatibility between a given pair of users
While it can be somewhat confusing to see both numbers when one is using OKC exclusively for dating purposes, some users indicate an affinity for the friendship number as a "counterbalance" to the flames of mutual lust that may arise… That is, a high Match percentage could indicate a strong romantic/initial interest, whereas the Friend percentage shows potential for a longer term,less sexually-focused relationship.
Assays, however, the validity of either percentage "on the ground" in real world settings is questionable, and until OKCupid/IAC release hard data on date outcomes/feedback/success rates tied back to these match percentages, it will be impossible to validate how accurate the underlying algorithms are.