E# (E
sharp) is a musical note commonly called
F.
It is called E# when it appears in some
scales and
chords, such as
A#.
The reason why it's called E# instead of F in some scales
is that
musicians like all scales to have one note with
each name from
A to
G. Therefore the
A# major scale
looks like this:
A# B# C## D# E# F## G## A#
As you can see, every note is sharp, and three notes
are
double sharp. This makes people unhappy, so it
is very rare to find a piece of music written in A#,
instead they are written in
Bb.