Abt bad links

bad links - in general links that are from sites with hight spam score, links that are from blog comments, or any pages that are full of other backlinks, you can check your links spam score in moz.

Bad link can be considered any link that doesn't serve the purpose of increasing rankings.

Bad link is generally harmful in one way or another..

Example:

- link from sites containing malware
- link from link farm with extreme OBL
- link for penalized / de-indexed website
- link with over-optimized anchor text

Unrelated, untrusted and even worse penalized sources, - that's usually where your bad links come from.

Easy to get some basic education on this with basic search but if you want to go crazy about it, check some tools that audit your baclinks profile and detail 'bad links' (think you can signup for a trial)