An approach to a corner stone along the fourth line (hence "high") and separated from it by two spaces.
For the two-point high approach to the 3-4 point shown here, the most normal answers are Black at a, b, c (3-4 point distant high approach, one-space low pincer). Black's tenuki is common, also. See 3-4 point distant high approach, tenuki, inside contact.
The outside contact play Black d is less common, but a rich source of less-explored pushing battle variations: see pushing battles in joseki 9.
Less usual answers are at d, e and f.
For d see light play example 1.
This approach was played in the nineteenth century, and became popular in Japan in the 1920s. It has recently been in fashion again.
Dieter: In the 58th Honinbo final, game 1, Kato Masao plays g against Cho U