A spike is a non-market quote caused by an unexpected failure in price delivery.
This is how a spike appear on the chart:
The signs of a non-market quote (spike) include, but are not limited to:
A significant price change within a few seconds
The price quickly returning to its original level
The absence of any notable news or market events
Since these prices are not genuine market quotes, any trades executed at spike prices are canceled, and the spike is removed from the chart.