What is the difference between ng-click and tap?

Can someone tell me how ng-click is different from tap? How is it implemented in Ionic?

Ng-click is an angular method that lets you bind to a function in your scope. The tap gesture is a way for you to create custom events based on that particular gesture. Most cases, ng-click fits peoples needs

Well not in my case at least. I need onmousedown and there is no support for this event in hammer.js and hence no support in Ionic also.

Well you could use the standard mousedown event, but we also have a hold even that you could use too.