The concept that many SEO experts lovingly call "Link Juice" is actually quite a fluid concept (no pun intended) and loose term. Link Juice generally refers to the power and potency of inbound links that point to a particular website.

Basically, if you have 5,000 links pointing in to your website, that amounts to a lot of link juice. That's just the amount of... juice. Now we talk about the potency of that juice. What if you had just 500 links pointing to your website, but each of those links were from extremely popular websites with high page rank? That would probably be about equal to or even better than the 5000 links, depending of course upon what kinds of websites were pointing to your website in each example.

As you can see, it's really hard to pin down a solid effect of "link juice". It really depends on each and every link you have - not the number of them necessarily. So, "Link Juice" is not only about the quantity of your inbound links, it's also about the quality of those links.

The lesson to be learned here is not only to take silly, metaphorical terms with a grain of salt, but also to realize that link building is about more than just the numbers. Quality matters!