Too many visitors pop into your home page for 2 seconds and then leave. You know how it is. We all do it when we are using the search engines. Either it wasn't the information we were looking for, or they had this huge graphic on this stupid portal page, which just took forever to load. These visitors shouldn't even count, but they get counted as 12-18 hits in your server logs.
Hits are requests to the server.
Reciprocal links bring in qualified visitors. These are visitors who were already on a web site which had matching Themes to yours. They already have a good idea of what type of site you are. They will come into your site and actually stay awhile. These visitors should count as double credit, they are so good.