Sorry @YouMightLikeCats . I thought you were on a wind-up.
For me, personally:
If I invite people for brunch or dinner or for a party or whatever at my house, I'm hosting.
If it's my birthday or another occasion and we invite people to celebrate with us somewhere else, to my mind that is our event and we will therefore pay for the guests invited, We would decide how many we can feasibly pay for and that will determine what we do, how and where! The same has always applied - whether it be a kids party at home, at a soft play or pottery place etc etc; an adult birthday party in a restaurant, bar, river boat; a graduation; a wedding or anniversary or whatever the case may be.
Some people on here take the view that you only 'host' if something is in your house, mainly on the basis that people don't expect them to pay in restaurants as it's too expensive and not the done thing in their social circle. I understand this, although I don't see the rigid distinction. Especially as it can actually be more expensive to have a dinner party at home than to host people in a restaurant.
In general, if you just say to friends, "let's go for a pizza on Saturday," you are not hosting because there is no occasion and you're all there just to socialise / fir a catch up. Nobody brings gifts. Nobody sings 'Happy Birthday' or makes a speech. It's just a normal meet-up.
If you want to buy a round of drinks or some sausage rolls or what-have-you in the course of a normal day, then you are doing just that. But if you were to say you are inviting people to a drinks party (or even a sausage-roll tasting party, for the sake of argument) then you are hosting - with the drinks and / or sausage rolls! You wouldn't ask people to a drinks party and then provide no drinks.