The <progress> element is similar to <meter> but it is used for progress bars (i.e., the percentage of a file being uploaded, etc.):
<progress id=pr value=50 min=0 max=100>
Gives
The browser calculates the percentage corresponding to the value, min and max attributes and adjusts the length of the progress bar accordingly.
If no value attribute is set, the progress bar will display an "indeterminate look", that may slightly vary among different browser implementations.
Here is an online example at JSBin.
This example uses some JavaScript to simulate a download progress by changing in real time the value attribute.
The progress below is defined like this:
<progress id=pr value=100 max=1000>
Source code:
Download progress: <progress id=pr value=100 min=0 max=1000></progress>
<script>
var i=0;
setInterval(function () {
i = (i+1) %1000;
document.getElementById('pr').value = i;
},1);
</script>