Spam. Don't abuse social gestures, send unwanted messages, or aggregate content in a less-than-meaningful way. Don't put tags on your posts that will mislead or deceive searchers (for example, tagging a photo of your car with "#lady gaga" and "#britney spears"); of course, meaningful uses are always fine (for example, ironic "punchline" tags that add to or playfully subvert a post itself). Don't put deceptive links or dubious code in your posts. That includes using Javascript to inject unwanted ads in blogs, or embedding links to interstitial or pop-up ad services. Don't use deceptive means to generate revenue or traffic, or create blogs with the primary purpose of affiliate marketing. Spam doesn't belong on Tumblr.