Some voters turn out at polling stations and then invalidate their ballots on purpose to express, for instance, their dissent with how elections are carried out. It could be expressed by making drawings on the paper or filling it in improperly. What do you call that in English? 'Intentional ballot invalidating' is certainly not how you say it.
What do you call it when a voter intentionally makes his ballot invalid in protest (by putting crosses in all boxes, for example)?
It's called spoiling the ballot. https://en.wikipedia.org/wiki/Spoilt_vote
1Does it imply the deliberate nature of that? Nov 24, 2019 at 23:07
3Yes, it does. If a voter gets it wrong and invalidates the ballot by mistake, that will still get counted as a spoilt ballot, but normally when we talk about spoilt ballots we mean those deliberately spoilt. Nov 24, 2019 at 23:09
In Australian English, it would be "informal voting". The term covers both deliberately and accidentally invalid votes, but depending on context it often implies deliberate.