In its simplest definition, discernment is nothing more than the ability to decide between truth and error, right and wrong. Discernment is the process of making careful distinctions in our thinking about truth. In other words, the ability to think with discernment is synonymous with an ability to think biblically.

1 Thessalonians 5:21-22 teaches that it is the responsibility of every Christian to be discerning: “But examine everything carefully; hold fast to that which is good; abstain from every form of evil.”

via Defining Discernment.