Multiple CSS and jquery

Problem Description

How does the meaning in class="errorMessage active"
HTML Code
<span class="errorMessage active">Invalid</span>


CSS Code and why the .active after the .errorMesage
.errorMessage{
display: none;
color: red;
margin-left: 10px;
}
.errorMessage.active {
display: inline-block;
border: 1px solid #e6e6e6;
padding: 0 5px;
background: #ffdae0;
border-radius: 3px;
}

Jquery code
$('.IncludeSnRNA').on('change', function(){
    if($(this).is(":checked")){
    $('.errorMessage').addClass("active");
    $('.IncludeSnRNA').val('t');
    }else {
    $('.errorMessage').removeClass("active");
    $('.IncludeSnRNA').val('f');
    }
    });

Solution

It is the Combinations of Classes and IDs

Target an element that has all of multiple classes

and means the active class of errorMessage class is use as constraint to that the subject is errorMessage