Refer to https://www.mclpcb.com/pcb-guide point 4, it is a decent description.
If you don’t want to check for slivers, you can disable the check in setup->violation severity. What is considered a sliver is hardcoded AFAIK, there is no setting you can change.
If you want to remove the cause on your PCB that can be tricky as the error markers are not always accurate.
There is an active bug report regarding slivers: https://gitlab.com/kicad/code/kicad/-/issues/14549
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Generally, you might have to play around a little to avoid situations like this:
