A preempt or pre-empt is a bid made in order to take up opponent's bidding space so that they cannot find the optimum contract. Weak two bids and suit opening made at the three level or above are preemptive openings.
Preempts are made by length rather than strength. The law of total tricks gives a good indicator on how high to preempt.
Preempts are rarely made at the pass-out seat, since there is no one to preempt.
This is a good 4♥ opening hand at the 3rd seat, since the 4th seat probably has many HCPs. Such bid takes the auction to game level and the 4th seat is very difficult to overcall at the 5 level.
This hand has no HCPs, however, in SAYC, after partner's 1st seat 1♠ opening, this is a good raise to 4♠, since the opponents are very likely to have 25 HCPs for game and this bid shuts their 4♥ game out.