A seed round funds the search for product-market fit. Seed companies usually have an MVP, early customers, and a credible thesis about who the product is for. Round sizes have crept up over the past decade: 'classic' seed is $2 to 4M, but seed+ rounds of $5 to 8M are common in hot sectors.
Seed investors are looking for early signs of product pull (retention, paid pilots, growing usage) and the team's ability to iterate to fit. Lead investors typically take 10 to 20% ownership and a board seat or observer role.