I play Tetr.io a lot.
If I send a large amount of garbage, it shows a number, followed by “spike”. What is a spike?
I have found nothing, here on the Arqade, or on Google; just videos of people doing spikes.
Edit: As of 28/09/2021, due to the 6.1.0 update, the UI has been updated so that the word "spike" no longer appears on the side of the board. Instead, when doing a spike, the garbage number simply appears larger and has a flashing animation.