what is subsequence in python code example

Example: subsequence python

def printSubSequences(STR, subSTR=""):
    if len(STR) == 0:
        print(subSTR, end=" ")
        return
    printSubSequences(STR[:-1], subSTR + STR[-1])
    printSubSequences(STR[:-1], subSTR)
    return

# Input : abc
# Output : a, b, c, ab, bc, ac, abc