a simple noob question

Hi i'm reading the book "C++ GUI Programiming with Qt4",and i found this code on chapter 2,my question is what the "emit" keyword does in the code,what is it for?

Code:

void FindDialog::findClicked()
 {
     QString text = lineEdit->text();
 Qt::CaseSensitivity cs =  caseCheckBox->isChecked() ? Qt::CaseSensitive
                                 : Qt::CaseInsensitive;
 
     if (backwardCheckBox->isChecked())
 {
         emit findPrevious(text, cs);
     } else {
         emit findNext(text, cs);
     }
}
 
 void FindDialog::enableFindButton(const QString &text)
 {
     findButton->setEnabled(!text.isEmpty());
 }