Bootstrap comes with 250+ glyphs that you can use as icons. See the full list here. Here's how to use them:
<span class="glyphicon glyphicon-trash"></span>Accessibility
Make things more accessible by using aria-hidden="true":
<span class="glyphicon glyphicon-trash" aria-hidden="true"></span>Buttons
Use a glyph in a button as follows:
<button type="button" class="btn btn-default">
<span class="glyphicon glyphicon-eye-open"></span> Button text
</button>