What is voting fraud?
Voting fraud is the systematic voting against correct voting rationales. Fraud most often happens with a single user continually voting (up or down) on many of your posts within a short period of time. This is not considered normal behavior and the system will not allow it.
If mass voting continues to happen between two certain IP addresses (voting each other up) or from a single user, or looks just plain suspicious in general, moderators and/or developers may investigate the matter and disciplinary action may be taken against the users involved with the fraud.
What is this meaning of highlighted sentence here?