Sounds like it simply means link exchange. But if you want to be sure, give us more information to go on (like the website you found that on, or the surrounding text).
Which google says is a no-no http://googlewebmastercentral.blogspot.com/2006/12/building-link-based-popularity.html
Link exchange is a no-no yes, but cleverly placed three or four ways on different c class IPs might fool G IT
Recently they said very specifically that they can find out about three ways. Four ways are probably easy to spot as well. Anything that's too symmetrical is likely to be easily spotted by google (they are math-wizzes, after all).