A tag used when there is no violence in the image.
Note that violence can happen in follow up images, and there can be the threat of violence in the image, and it will still qualify for this tag. As long as there is no violence in the actual image, it gets this tag. This is used to distinguish between family friendly, and parts of series which may appear to be family friendly/have parts of it, but turn to violence later. The use of this system helps to prevent those who dislike violence and greatly favour family friendly running into things that will upset them.
Use discretion when commenting on some non-violent images, namely those that barely failed getting the FF tag. Some users will treat these like FF images, and it may lead to problems. However, they are still _not_ FF images (and hence will be treated by some other users as not) and the rules apply to FF images (for good reasons partially stated above and elsewhere); it's best just to follow them. Though using your common sense when commenting is always a good thing to do.
Also note that by default, all FF images are non-violent.