The symbol frequencies in all sequences were counted in both sets. The column names represent the symbols, for example by comparing amino acids you'll find the amino acid one letters as column names.

Row descriptions:

abs1: Absolute number this symbol was found in all sequences of set 1
rel1: Relative number within this value range of set 1. (Relative to all elements of set 1)
abs2, rel2 analogous
diff: Difference between the relative fractions: rel1- rel2

 

Description of set 1: '$SETA'
Description of set 2: '$SETB'