Dear NoahsMom,
To try and get the biblical perspective on "rebuke", I looked it up in the modern dictionary. The definition of "rebuke" is to "reprimand or criticize". A synonym for both of these words is "admonish", which means "to warn".
I believe that when we come across the word "rebuke" in Scripture, most often it means to point out sinful behavior in a person, or group of people, and warn them that they should repent of that behavior and change their ways. For example, in his letter to Titus, Paul said "It teaches us to say “No” to ungodliness and worldly passions, and to live self-controlled, upright and godly lives in this present age, while we wait for the blessed hope—the appearing of the glory of our great God and Savior, Jesus Christ, who gave himself for us to redeem us from all wickedness and to purify for himself a people that are his very own, eager to do what is good. These, then, are the things you should teach. Encourage and
rebuke with all authority. Do not let anyone despise you." (Titus 2:12-15, emphasis added)
The next most common usage, in my view, is "to criticize". As in Matthew 16, verse 22, which says "Peter took him aside and began to rebuke him. 'Never, Lord!' he said. 'This shall never happen to you!'” However, I don't think you could go too far wrong if you substitute the word "admonish" each time you see "rebuke".
Have a blessed day!