A player only bets the minimum bet. Popular when playing strong hands in an early position in order to respond to raises with re-raises. In a later position - if nobody has raised - it gives a player with a weak hand the chance to see the flop without putting down too much money.
Preflop Raise:
A strong hand should be raised accordingly. A 3-fold or 4-fold raise of the Big Blind puts a lot of pressure on the other players. This is useful in two ways: It brings more money into the pot, plus some oppenents may drop out. This raise aviods that currently medium or weak hands enter the game that later on still could become strong hands.
Blind Stealing:
If a player is the Dealer button and no other player has entered the game before, a raise against both Blinds can be effective. Demonstrated strength at the Dealer button will often scare the Blinds off. Blind Stealing is often played as a Bluff and can even be used by the Small Blind against the Big Blind.