A
directory within a
filesystem which appears within another directory. Obviously, every directory except the
root directory is a subdirectory of some other directory, which is usually referred to as its "
parent directory".
A pictorial example to explain these concepts:
_ / _
/ \
home usr
/ \ \
mel jason bin
/ \
bin porn
Here,
home and
usr are subdirectories of
/, and also pictured are two subdirectories of
home and one subdirectory of
usr. Unlike the author's actual computer, the directory
/home/jason is the parent directory of
porn (in reality, it's hidden way further down in the
directory tree than that).