Neapolitan Chord
A major chord built on the flat 2nd scale degree

It will have a lowered 2nd scale degree and a minor* 6th scale degree
*(in a major key, 2 and 6 will both be lowered)
*(in a minor key, 2 will be lowered but the 6th scale degree is already minor)
It is typically found in first inversion
It is labeled N6

Sometimes it is found in root position or second inversion

It usually resolves to V or I64
In a major key, care must be given to voice-leading to avoid parallel fifths resulting from the resolution of the two active (altered) tones