I am little confused with the term susequence.Specifically is “abcdef” a subsequence of “abcbdef” as it can be obtained by removing the b ocuuring in the middle of string?
yes.
“abcdef” is a subsequence of “abcbdef”…
A subsequence of string is a string obtained after removing some characters of string and order of remaining characters should be same as it was in original string .