A movable chord shape is a chord formed on the guitar that can be moved anywhere up or down the fretboard to form the same chord type with a different root. This is only possible if the shape contains no open strings. For example, if you were to shift every note in the G major chord (shown below) up one fret, you would still have a major chord, but in this case it would be G♯ major:

Here’s a practical example: Lets say we wanted to play a B major chord. Since our root note for the chord shape (shown in blue) is on the d-string, all we need to do is find B on that string:

Since B is the 9th fret of the d-string if we apply the shape from before, but starting at this point, we end up with a B major chord: