Redundant content is the one people will find everywhere on the internet. This content mostly is a subject of content duplicating. If you ever duplicate some popular contents to get some traffic or SEO, delete those contents now. Content duplicating can trigger Google spam alert, and your site will lose the rank. So if you find any interesting content from other site, don’t duplicate it, just link it.
Outdated content means new content that refers to something old. Like mentioning some already recalled product, or mentioning an already closed down web agency. This will obviously ruin your site’s credibility. Again, bad user experience. What about your old page? Well, old page archive is better to be kept alive.
Trivial content is content that provide no useful information. We’ve talk about this before.