When search engine spiders like Googlebot visit websites they use specific user-agents, webmasters can use Googlebots user-agent to serve Google content NOT served to other visitors. If you are contemplating using black hat SEO link cloaking, consider when caught your site will receive a Google penalty!
For example you might have links in an image-map, image-map links can not be indexed by Google, so it would be acceptable to serve Googlebot those links in another format like text links. General visitors see the links in an image-map, Googlebot sees them as text links or standard image links (a clickable image link).
As long as a general visitor and Google sees pretty much the same content AND you aren’t gaming Google, it’s acceptable to use cloaking.