target="_blank" vs. target="_new"

Use "_blank"

According to the HTML5 Spec:

A valid browsing context name is any string with at least one character that does not start with a U+005F LOW LINE character. (Names starting with an underscore are reserved for special keywords.)

A valid browsing context name or keyword is any string that is either a valid browsing context name or that is an ASCII case-insensitive match for one of: _blank, _self, _parent, or _top." - Source

That means that there is no such keyword as _new in HTML5, and not in HTML4 (and consequently XHTML) either. That means, that there will be no consistent behavior whatsoever if you use this as a value for the target attribute.

Security recommendation

As Daniel and Michael have pointed out in the comments, when using target _blank pointing to an untrusted website, you should, in addition, set rel="noopener". This prevents the opening site to mess with the opener via JavaScript. See this post for more information.

Using target="_blank" will instruct the browser to create a new browser tab or window when the user clicks on the link.

Using target="_new" is technically invalid according to the specifications, but as far as I know every browser will behave the same way:

• it will search for a tab or window with the context name "_new"
• if a "_new" tab/window is found, then the URL is loaded into it
• if it's not found, a new tab/window is created with the context name "_new", and the URL loaded into it

Note target="_new" will behave exactly the same as target="new", and the latter is valid HTML while the former is invalid HTML.

Adding some confusion to this, in HTML4 the target attribute was deprecated. In HTML5 this decision was reversed, and it is an official part of the spec once again. All browsers support target no matter what version of HTML you are using, but some validators will flag the use as deprecated if your doctype is HTML4.