ALDF – Average Logarithmic Distance Frequency

is a modified frequency that prevents the result from being excessively influenced by one part of the corpus (e.g. one or more documents) that contain a high concentration of the token. If the token is evenly distributed across the corpus, ALDF and absolute frequency will be similar or identical. Compared to ARF (Average Reduced Frequency), ALDF is calculated from the average distances between tokens rather than their frequency.

see also ALDF definition