What is the meaning of onsubmit="return false"? (JavaScript, jQuery)

This is basically done to handle the form submission via JavaScript.

For example - for validation purposes

See the below code and see how it can be beneficial:

<script language="JavaScript">
myFunctionName() {
    if (document.myForm.myText.value == '')
        return false;
        // When it returns false - your form will not submit and will not redirect too
    else
        return true;
     // When it returns true - your form will submit and will redirect
// (actually it's a part of submit) id you have mentioned in action
}
</script>

<form name="myForm" onSubmit="return myFunctionName()">
<input type="text" name="myText">
<input type="submit" value="Click Me">
</form>

If you are using a button instead of submit as in my case below:

 <form name="myForm" onSubmit="myFunctionName(); return false">
    <input type="text" name="myText">
    <input type="button" value="Click Me" onclick="myFunctionName()">
 </from>