ASL = Average Sentence Length
AWL = Average Word Length
Tokens = the total number of all occurences of alphanumeric symbols
Word Types = the total number of distinct words (e.g. 10 instances of ‘do’ are counted as 1 TYPE of ‘do’.)
Lemma Types = the total number of base forms (e.g. ‘do’ is the lemma for do, does, did, doing, done if any).
Lemma/Word ratio, Word TTR (Type Token Ratio), Word STTR (Standardised Type Token Ratio), Lemma TTR and Lemma STTR are all scores for lexical richness. Most often Word STTR is good enough as a lexical richness value. You can use the other scores for your particular research purposes.