To say the same thing — from homos (same) + legō (to say). Confession is agreeing with God's assessment: of sin (1 John 1:9), of Christ (Rom 10:9), and of truth before others.
Confession has two directions: confessing sin (agreeing with God that it is sin) and confessing Christ (publicly declaring him as Lord). Both are forms of aligning one's words with reality.
The two great confessions — of sin and of Christ — are the Christian life in miniature: owning our failure and owning our Savior. Matthew 10:32 raises the stakes: earthly confession of Christ determines heavenly acknowledgment.