What does this syntax mean <# #>
in a script?
<#for (i in data) { #>
<# if ( ! data.hasOwnProperty( i ) ) continue; #>
<# field = data[i]; #>
<# if ( ! field.type ) continue; #>
This notation is used for templates in the source code of Kirki, a Wordpress tool. You might be familiar with other template tag variations such as <% %>
(Rails).
I assume that the snippet from your image is taken from this file.