ASPX in-page expressions are, if you don’t know what to call them, nearly impossible to search. So on the off chance that this helps somebody, here are some search-friendly terms that might one day get crawled; (less than percent hash), (less than percent equals), (in-page expressions), (data binding), (data bound), (bee strings), (asp.net server tags), (code render blocks)
<% %>is for inline code (especially logic flow)
<%$ %>is for evaluating expressions (like resource variables)
<%@ %>is for Page directives, registering assemblies, importing namespaces, etc.
<%= %>is short-hand for Response.Write (discussed here)
<%# %>is used for data binding expressions.
<%: %>is short-hand for Response.Write(Server.HTMLEncode()) in ASP.net 4.0+
<%-- --%>is for server-side comments