SPX
has had experienced 10 corrections in 2021. 4 out 10 were as little as 2 - 2.5% and last 3 - 5 days. 
Bigger corrections were as big as 3.2 - 5.75%, last between 4-12 days. Correction 3,6, and 10 crossed below the previous low (lowest level of the previous correction).
If you are looking at 3rd and 6th corrections, you see several strong rebounds (Green candle with long bodies) during these corrections. These rebounds were as big as 1.3 - 2.4 %.
The biggest difference between the 10th Correction with the previous big corrections is:
1- in the past 12 days, we do not see any meaningful rebound, one was +0.23%, and the other one was +0.85%.
2- Red corrective candle's bodies become bigger and bigger.
3- We don't see long upper or lower shadows, and in 10 out of the last 12 days candles finished the day lower than the openings.
To wrap it up, we are just 4.35% away from the top and this must be considered as a correction, however, you should not forget that this is the longest bullish run ever and the longest time in S&P 500 history without a 10% or more correction.
Best,
Moshkelgosha