Wikipedia says:  
the set of activities that are associated with making decisions in groups, or other forms of power relations among individuals  

Merriam-Webster (My personal favourite) says:  
competition between competing interest groups or individuals for power and leadership (as in a government)  
and:  
the total complex of relations between people living in society  

Collins says:  
the actions or activities concerned with achieving and using power in a country or society.  
and:  
the ways that power is shared in an organization and the ways it is affected by personal relationships between people who work together  

So, anything having to do with power or decision making within a group of people is politics. When you and your mates decide which takeout place to order from, the decision follows a political process. When your parents told you it was bed time, they used political power. When you come to trust someone’s opinion in guiding your personal decisions (like whether you should really include the chapter on bird mating calls in your work in progress fantasy novel), you’re engaging in politics.

Politics is all around us. It’s ridiculous to have a negative opinion of it. If there were no politics, there would be no societies, no families, no friendships, and no romantic relationships, because there would exist not a single mechanism for any group to have unified purpose or choice.

Unless you misdefine politics. That’s the trick. And it’s a very easy trick, you can do it without noticing. All you have to do is think in the back of your mind “politics is anything I disagree with”.

Boom. So long as you have the rhetorical skill or the social power to defend this assertion, you can take advantage of the propaganda of the ruling class for your own ends, and attack any goddamned idea in the world you want. You have an intrinsic claim to legitimacy in proportion with your ability to normalise your own opinions, and anyone who disagrees with you is committing “violence”. You have a terrible and destructive power to silence any and all dissent. What you say will go. Nobody can stop you.

What I have described just now is the worst extent of the power of belief in apolitics. Most people who believe in apolitics won’t act this way… if you don’t push them. If you keep agreeing with what they say in a vague sense, or phrase your disagreements charismatically, they won’t use this power. But it’s still there. And there is no sense at all in leaving around terrible powers that reinforce hierarchies of norms. Especially not if you are queer, neurodivergent, disabled, of colour, otherkin, or anything else that goes against the status quo. Because in a battle to attack the political, that which can claim legitimacy through normalcy will always win.