Whats the difference between # and $ in ELs in ADF

[dr.robo]

Have a really basic question on the difference between # and $ while evaluating ELs.Ex. \[code\]<c:if test="#{bindings.value =http://stackoverflow.com/questions/15741793/= true}">\[/code\]and \[code\]<c:if test="${bindings.value =http://stackoverflow.com/questions/15741793/= true}">\[/code\]