A seed is a positive integer assigned to a participant in a Bracketed Heads-Up Standard Tournament that determines their initial match placement in the bracket. Seeds will be used to match the highest seed against the lowest seed, the second-highest seed against the second-lowest seed and so on.
Note that brackets are ideally suited for a number of players that is an exponent of 2: 2, 4, 8, 16, 32, 64, etc. If the number of players in your tournament is not an exponent of 2, then the highest seeds will receive byes in the first round (the NFL playoffs are an example of this).