Membership based on intent to follow a DAO

On Snapshot there is a notion of "members", from the interface snapshot.org you can click "Join" button from a space (DAO) page to be a member of that space, this is something that anyone with a logged wallet can do, it doesn't require any permission, and this give you a way to subscribe to see proposals in a feed (similar than following someone on Twitter) and also receive notification for that specific space every new active proposal.

Membership based on voting power

We can imagine also that the ability to vote on a proposal can also be considered as a membership, and for this on Snapshot the users able to vote on a proposal are simply the ones having voting power. Voting power is defined on Snapshot on the space and proposal level with "voting strategies", these voting strategies are JavaScript scripts that take the list of voters as input and return as output a voting power for each of them. It can be the balance of an ERC20 or some more complex strategy like taking voting power from token held in Uniswap pools. Here is more info about strategies : https://docs.snapshot.org/strategies/what-is-a-strategy