A spike is a non-market quote.
On the chart, a spike may look as follows:
Indications of a non-market quote include but are not limited to:
a significant change in price within a few seconds
the return of the price to its original level
lack of a characteristic news background
The main reason for a non-market quote is a technical failure.
For example:
The liquidity provider sends the following price flow to the broker: '99.00; 100.00; 100.00; 101.00; 100.00; 99.00'.
As a result of a technical error, the flow looks like '99.00; 100.00; 100.00; 10.100; 100.00; 99.00'; therefore, we see a 'falling' movement on the chart for 1 second. Since the prices are non-market, the trades made on them are cancelled, and the spike on the chart is deleted.