That is one definition of racism, but it is not even the most common definition. Individuals can be racist/perform racism. You don't get to change the definition that most people use just because you don't agree with it. Check the dictionary, you will clearly see that "racial prejudice or discrimination" is right there.

Racism is a term which has become fairly muddy without a specific definition. You say it's the systematic oppression of people. Wikipedia says it's "the belief in the superiority of one race over another". Others say it's prejudice + power. We could go on for a while.

This arguing about what the word exactly means is a waste of time.

Who says racism exits ONLY against black and brown people? Historically, it has existed against Jews and Asians.

The admission policy of Harvard (an institution) has been used against Jews, now it is used against Asians. By your definition, it is racism.

I'm not sure copy-pasting this argument 5 times in the thread has made it any more convincing.

There's a tendency in many fields to take a piece of jargon specific to that field and insist that non-members of that field also use it the same way. Forming jargon is healthy in a field but trying to enforce it outside the field isn't. A biologist who tries to correct you when you talk about an octopus having tentacles is wrong to do so. And a critical race theorist correcting you when you say that James Strom Thurmond was racist is equally wrong.

Since you posted this exact statement a dozen times. Could you answer, What exactly is the benefit for white people to be racist to black and brown people?

They're so many: being able to get a home loan (redlining), not being killed by police even when you have a gun, having access to generational wealth, being promoted and included in instutions of power and wealth that are run by white people, having family or friends being able to get you high paying jobs because they and their parents were similarily employed, seeing images of people that look like you portrayed as the hero/savior/good guy in media, living in school districts that ate better funded, not having people target or attack you for your skin color, not having laws that were created to incarcerate you (war on drugs, the numerous new Jim crow laws) etc.

And I see that your question implies a confusion: a white person needs to do nothing to participate in racism. By being white, going with the flow means receiving the benefit of these insutions. A white person could never act in a racially discriminatory way and still receive benefit.

White people need to actively dismantle the system that is racism so that it no longer benefits them. (This is the only ethical path forward.) And if white people are scared that they'll be treated the same way that they treated non white people, then they should ensure that the dismantling doesn't prop up a new oppressive system.