This is the last 5 days of the S&P 500:

Source: Prophet.net

From Elliottwave.com:

Ending Diagonal

An ending diagonal is a special type of wave that occurs primarily in the fifth wave position at times when the preceding move has gone “too far too fast,” as Elliott put it. A very small percentage of ending diagonals appear in the C wave position of A-B- C formations. In double or triple threes (see next section), they appear only as the final “C” wave. In all cases, they are found at the termination points of larger patterns, indicating exhaustion of the larger movement.

Ending diagonals take a wedge shape within two converging lines, with each subwave, including waves 1, 3 and 5, subdividing into a “three,” which is otherwise a corrective wave phenomenon. The ending diagonal is illustrated in Figures 8 and 9 and shown in its typical position in larger impulse waves.