Define THE WORD ABUSE?

report abuse, many Q&A,of websites,posts of communities,friendshipsites all have those two words.Who decides the correct meaning?The one asking question,or the one answering?or the members/or the moderator?The moderator,does he/she monitor all the entries all the time?And what is abuse in a community? or in Romance and relationship group? Why bar or block a violater from all other groups?or prevent interacting with others?