A sequence of honour cards (including the 9) that comprises two or more touching cards with one higher non- touching honour.
For example, A-Q-J, K-J-10, Q-10- 9. The standard lead from an interior sequence is the highest of the touching cards, ie the queen, jack and ten respectively.
Here is the interior sequence lead in action:
After West leads the ten and dummy plays low, East can withhold the king, allowing the defenders to finesse against dummy’s jack. Had West led a fourth best six, East would have to put up the king to stop the eight from scoring, setting up the jack as a third- round winner.