Corpus Term Frequencies shows overall word frequencies for the entire corpus as well as information about how word frequencies are spread out over documents within the corpus. Hover over column headers and buttons for more information.
Document Term Frequencies shows word frequencies for each document in the corpus. You can see the selected word at the top of the window highlighted in yellow. Its relevance to the documents is shown in the table below.
ABFREQ was a tool for identifying key words within a text developed in the 1980s. It identified key words by comparing thier frequency within the user's text to the frequency of the same words in a control corpus.