Intrusion detection and density-based methods
Here is a formal definition of outliers formalized based on concepts such as, LOF, LRD, and so on. Generally speaking, an outlier is a data point biased from others so much that it seems as if it has not been generated from the same distribution functions as others have been.
Given a dataset,
D, a DB (x, y)-outlier,
p, is defined like this:
The k-distance of the
p data point denotes the distance between
p and the data point,
o, which is member of
The k-distance neighborhood of the
p object is defined as ...