It means you could literally have multiple 10+ loss in a row situations, many many times 15+ in a row as well all in the same run. Martingale is just not something that profits anyone, there is nothing to gain from martingale and nobody should do it. For some reason people are still using martingale to make money and I do not get why they do that but I still think that it is quite noobish to lose your money that way.
The reality is that no matter how careful you are with your martingale, no matter how you calculate yourself to endure 20 losses in a row and arrange the base bet accordingly, you will see hit that 20-21 in a row, that is just the reality. I am not saying that you will hit it right away, it make take time, who knows maybe you will have hundreds of thousands of bets before you hit it and make some profit that way and assume that you will not lose, there are tons of people that believe that, and maybe your base bet and not losing streak will help you reach all the way to 22-23 losses freedom, but eventually even that will happen.
The main story here is that no matter what you do, in the end one day when you are gambling you will hit that, if you gamble long enough (millions of times) even 50 times in a row is possible, it is not impossible, so that there is nothing you can do to prevent a total loss no matter how you arrange it. Since there is a house edge against you, there is nothing you can do to make profit in the long term and it will stay like that.