stopwords, and 2-character and smaller words are excluded
This is the default. It can be changed from the Settings page. One can look at the list of stopwords.
Consider the following counters from the current collection.
Words: 388, Word count: 678, All words count: 1072
388 is the number of unique words (without the excluded ones).
Word count of 678 is how many times these words are used.
All words count of 1072 is the count of all words (including the ones discarded from the list).