Christians who study more in depth, could you explain the meaning of 'repentance'?

Repentance means to change one's mind. As in Acts 2:38, Peter tells the unbelieving Jews to 'Repent' in response to their question of what they must do to be saved. He's not telling them "stop sinning" in order to be saved. That's putting the horse before the cart. He's telling them to have a change in mind concerning the person of Christ, whom these very people had previously rejected and blasphemed.