Two Spirit is a non binary identity with a specific cultural context within the history of indigenous peoples. In Canada, due to the increased focus on dealing with the reconciliation of Indigenous peoples the current Acronym is 2SLGBTQIA as it sort of symbolicly puts precedent on amplifying indigenous voices in the movement.
Most places in the world recognize two genders and their respective social roles: men and women. Some places recognize a third gender and its respective social and/or ceremonial role. This is the case for (some) North American Indigenous people, and two-spirit is a catch-all term to refer to a third gender role that they recognize.
It's hard to map onto the more standard two gender system that most of us are familiar with. When you think of men as the breadwinners and women as the child bearers, some cultures think of an additional distinct third gender with a designated social/ceremonial role.
But as you might have thought while reading that, men being the breadwinners and women being the child bearers is already a fairly outdated view of gender and social roles. Turns out social constructs are messier than they seem when you start to really analyze them and attempt to strictly define them.
TLDR: two-spirit is a catch-all term for a type of queer identity recognized by some North American Indigenous cultures.
It's reductive, but still close enough if you don't know/interact with nonbinary or two-spirit people on a regular basis. At least to the extent of my understanding.
AFAIK, it's basically people with different spirits inside them, falls in the gender queer domain, like being trans/NB (not a sexual orientation). So someone could have a male spirit and female spirit, or a female spirit and a nb spirit.
It primarily seems to be a First Nations/Native American identity, and appears to have a decently long history throughout time.
Two spirit in a Canadian Indigenous context refers to people who identify as having two spirits inside of them. They have the spirits of both a man and a woman, so outside Indigenous culture I think the most related term would be non-binary.