What does Angular 2 hashtags in template mean?

It’s syntax used in the Angular 2 templating system which declares DOM elements as variables.

Here I give my component a template URL:

import {Component} from 'angular2/core';

@Component({
   selector: 'harrys-app',
   templateUrl: 'components/harry/helloworld.component.html'
})

export class HarrysApp {}

Templates render HTML. In a template you can use data, property binding and event binding. This is accomplished with the following syntax:

# – variable declaration

() – event binding

[] – property binding

[()] – two-way property binding

{{ }} – interpolation

* – structural directives

The # syntax can declare local variable names which references DOM objects in a template.
e.g.

 <span [hidden]="harry.value">*</span>
 <input type="text" #harry>
 {{ harry.value }}