Landfall is an ability word: it has no rules meaning of its own. It labels a group of triggered abilities that share one pattern. The Oracle examples all use the same frame — Landfall — Whenever a land you control enters, … — though the payoff differs: gaining energy, investigating, or becoming prepared. The label groups them; each card's actual rules text defines what happens.
That shared pattern matters because it turns land drops into extra triggers. A Landfall deck can use fetch lands, ramp spells, or extra land plays to trigger several abilities in one turn, so its payoffs often scale with how many lands it can put onto the battlefield. The ability word makes those cards easy to recognize and build around, even though the abilities themselves are separate.
