When entered into Google, what's the difference between "link:www.mysite.com" and "links:www.mysite.com"?

Question

I've heard this is the way to measure inbound links to a website? What is the difference between the two and is there a better way besides these?

Answer 1

links: is not a Google Search operator, so it is equivalent to just use the word link as an additional keyword in the search. The proper operator to use is link:, not plural.

Answer 2

I've heard this is the way to measure inbound links to a website?

It's a way to get a feel for it.
Arguably Google would prefer that you do it via their Webmaster Tools, where you'll find it under Traffic->Links to Your Site. The link: operator only shows you a selection of results like site: does. (Mentioned at that previous link.) Webmaster Tools is also a better option for this as it provides some extra information like who links to you most, and how your site gets linked to.

Note that if you do continue using the link: operator, Google recommend using the domain name without the www sub-domain. (They're not the same thing.)

[EDIT]
On further review using a domain I control and so could do a better job filtering, it looks like non-existent search operators, eg links: just get ignored and treated as a literal strings as much as possible. It'd be nice if they popped a warning message about this. But for example, if you do a search for "foo:rottentomatoes.com" you'll see results up top for things like the movie "To Wong Foo…" and the actor John Foo, plus even attempts to figure out if your search was a typo, eg. "Kung Fu Panda" also shows up.