Because of some confusing text in the PH, some people think there's not much difference between being incorporeal and being ethereal, when they're actually quite different (although some of the effects are similar). Ethereal is like incorporeal "taken to eleven"....

Incorporeal creatures are on the Material Plane, ethereal creatures are adjacent to the Material Plane. If the Material Plane is your house, an incorporeal creature is like a paper cutout of a person, while an ethereal creature is the real person, outside, looking through a tinted window.

Let's check the bullet points in the DMG describing incorporeality, and see where the incorporeal differs from ethereal.

    Incorporeal creatures can only be harmed by other incorporeal creatures, by +1 or better weapons, or by spells, spell-like effects, or supernatural effects. They are immune to all nonmagical attack forms. They are not burned by normal fires, affected by natural cold, or harmed by mundane acids.

Ethereal creatures can be harmed by creatures that aren't ethereal (with force effects, gaze attacks, or abjurations). They are not immune to all nonmagical attack forms (assuming they originate from another ethereal creature). They are burned by fire, affected by cold, or mundane acid, as long as that fire/cold/acid is on the Ethereal plane with them (not Material Plane fire/cold/acid).

    Even when struck by magic or magic weapons, an incorporeal creature has a 50% chance to ignore any damage from a corporeal source--except for a force effect, such as magic missile, or damage inflicted by a ghost touch weapon.

Irrelevant, since we've established that ethereal creatures have no actual immunity to certain attacks as long as those attacks come from the Ethereal plane. And unlike incorporeal creatures, ethereal creature's aren't affected by ghost touch weapons (unless, of course, you're on the Ethereal plane, at which point the weapon works just as well as if you were hitting an orc).

    Incorporeal creatures move in any direction (including up or down) at will. They do not need to walk on the ground.

Yep, that's the same. There is no direction or "ground" on the Ethereal plane except when there's a large object nearby.

    Incorporeal creatures can pass through solid objects at will, although they cannot see when their eyes are within solid matter.

Yep, that's the same, as long as that "solid object" is something that's on the Material plane (ethereal creatures cannot walk through ethereal objects, but Material Plane objects are in another dimension and aren't obstacles).

    Incorporeal creatures are inaudible unless they decide to make noise.

Ethereal creature's are inaudible to creatures on the Material Plane. They can't be heard even if they want to. To other creatures on the Ethereal plane, however, ethereal creatures make noise normally (otherwise if your whole party was on the Ethereal plane, you couldn't speak with each other).

    The physical attacks of incorporeal creatures ignore material armor, even magic armor, unless it is made of force (such as mage armor or bracers of defense) or has the ghost touch ability.

Ethereal creatures can't affect creatures on the Material Plane at all! They affect other creatures on the Ethereal normally, though.

    Incorporeal creatures pass through and operate in water as easily as they do in air.

Same, assuming we're talking about an ethereal creature passing through water on the Material plane.

    Incorporeal creatures cannot fall or suffer falling damage.

Same, since there isn't gravity on the Ethereal.

    Corporeal creatures cannot trip or grapple incorporeal creatures.

Material creatures cannot trip or grapple ethereal creatures, and vice versa.

    Incorporeal creatures have no weight and do not set off traps that are triggered by weight.

Same, since there isn't gravity on the Ethereal and they're not touching the Material plane.

    Incorporeal creatures do not leave footprints, have no scent, and make no noise unless they manifest, and even then they only make noise intentionally.

Ethereal creatures do have scent, it's just that creatures on the Material plane can't smell them across the planar barrier. A creature on the ethereal plane can smell another ethereal creature just fine. And again, ethereal creatures (except ghosts) don't have the inherent power to manifest and can't make noise on the Material plane while they're ethereal.

Just remember that an ethereal creature is a creature in another, nearby dimension. Creatures on the Material plane can sometimes see creatures in that dimension, and can actually reach them with force effects, but that's the only sort of interaction possible without using magic that specifically crosses planes.

So, ethereal and incorporeal are not the same thing.