unknown "<#" construct in javascript -

i'm newbie in js.. found construct i've never seen , although googled little, haven't fount info:

here piece of code found slider revolution:

<script type="text/html" id="tmpl-attachment-details-two-column">     <div class="attachment-media-view {{ data.orientation }}">         <div class="thumbnail thumbnail-{{ data.type }}">             <# if ( data.uploading ) { #>                 <div class="media-progress-bar"><div></div></div>             <# } else if ( 'image' === data.type && data.sizes && data.sizes.large ) { #>                 <img class="details-image" src="{{ data.sizes.large.url }}" draggable="false" />             <# } else if ( 'image' === data.type && data.sizes && data.sizes.full ) { #>                 <img class="details-image" src="{{ data.sizes.full.url }}" draggable="false" />             <# } else if ( -1 === jquery.inarray( data.type, [ 'audio', 'video' ] ) ) { #>                 <img class="details-image" src="{{ data.icon }}" class="icon" draggable="false" />             <# } #> .... </script> 

what used for? what's rules? thanks

this isn't javascript, see type="text/html"? html template.

see what modern uses of script type="text/html" , example considered use? (among other similar questions).