This is the default serif font. It is commonly used in printed media for better readability, since letters are more distinct in serif fonts.

<p class="nice" id="sans-serif-text">This is a sans-serif font. 
It is commonly used in screens because it is hard
for screens to render letters with such great detail.</p>

<script>
    var sansSerifText = document.getElementById("sans-serif-text");
    sansSerifText.style.fontFamily = "sans-serif";
</script>