Unequally yoked
Here’s what it means
Believers must not enter binding partnerships that join them to idolatry or fundamentally compromise loyalty to Christ.
Why the Bible says it this way
The writer uses a picture to explain one thing by describing it as another.
A helpful detail: The yoke image comes from mismatched animals. The passage is broader than marriage alone but should not be used to forbid every contact with unbelievers.