Target="_blank" is what you append to your a tag so that the link opens up in a new tab.
It all seems like fun and games untill a fellow web developer, in this case David Peach (co-worker and 'lets do things the right way - entrepanour') opens your eyes to the utter wrongness of using this feature as we all commonly do.
It's one of those little things that has become so common to use everywhere around your site, that everyone uses it - for everything. Using target="_blank" in a link means your site wont close when visitors click it to visit an external site, it will still be kept in a tab. At first it makes sense, as it stops vistors detering from your site, and this is why its so commonly used.
Its normally used on things such as social media icons and external referances. However the visitor didn't choose to keep your site open, they chose to leave.
If your visitors choose to leave your page via a link on your page, let them leave.
This is all just a matter of opinion. But I think, whether it's inbound or outbound links, you shouldn't be forcing your users to still have your site open in a previous tab, it's deemed insulting. It's also now depreciated, meaning one day, it wont open a link up in a new window.
There sre times when this feature can be useful, but it shouldn't be by default. There are default keyboard shortcuts which enable you to open a link in a new tab, as well as clicking the mouse scroll wheel which is very useful.
An example of using target blank the right way would be for instance, filling out forms where half way through, a window needs to open, without taking you away from the page so you dont loose all your previous input.
After reading a really good article from CSS Tricks, I went back and removed a load of target blanks from my site. It's not a major thing however, its just not best practise to be using them on every single link.