A bounce is a visit to your website that doesn’t result in a second pageview or a desired action. If your site participates in affiliate marketing programs such as Google AdSense, an outbound click may very well be your desired action.
To be able to properly optimize your website and your marketing campaigns, you need to differentiate someone clicking out on an affiliate link from someone who doesn’t find what they are looking for and just leaves. The “proper” way to do that is to either track them as pageviews, with the benefit of being able to tag them as goals but with the disadvantage of inflating pageviews, or as an event.
Joost de Valk talks about tracking affiliate clicks.