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: 7841, Word count: 47528, All words count: 73053
7841 is the number of unique words (without the excluded ones).
Word count of 47528 is how many times these words are used.
All words count of 73053 is the count of all words (including the ones discarded from the list).