Hey @EdZ good question. What it means in practice structurally can vary quite a bit. An ETF could track 2 stocks but that doesnāt mean that 1 share matches up to 1/2 a share of each company. Thatās all dependent on how many shares the ETF has issued vs the stake it has in those companies.
Also you wouldnāt own shares in those companies - you have exposure but not ownership
The best analogy is that an ETF is its own public company, but whose only purpose is investing in other companies. The performance of that company is a proportional aggregate of its investments.