Entity laws are all state-by-state in the US, but in most (all?) states, LLCs and corporations are essentially the same ownership-wise. A person buys membership interest/stock in an LLC/corporation, and becomes a partial owner. The organization is a separate legal entity then owning the contributed assets and the members/shareholders own the LLC/corporation. The bylaws will lay out how to divest a member/shareholder of his interest, usually involving the other members/shareholders or a board of managers/directors voting to buy out his shares.

It's not really a union of assets nor people though. The former would be a trust or arguably a non-profit, and the later would be a partnership. And LLCs can elect to be taxed as a C corporation, although I can't fathom why one would. (And most small businesses can elect pass-through taxation!)

No. Taxation of an LLC is not pass through. Taxation of a single member LLC that is a disregarded entity can be pass through. LLCs can also opt for sub K, sub S or sub C.

I also would not refer to an LLC as a collection of assets for a common purpose; instead I would say it is a popular entity form that limits member or manager liability. However you could take a different view.