a modified frequency that prevents the result to be excessively influenced by one part of the corpus (e.g. one or more documents) which contains a high concentration of the token. If the token is evenly distributed across the corpus, ALDF and absolute frequency will be similar or identical. In comparison with ARF (Average Reduced Frequency), ALDF is calculated from the average distances between the tokens, not the frequency of the token.
see also ALDF definition