These three trip people up constantly, so let's sort it properly.
Estate Emulsion is the finish that made Farrow & Ball famous. It's a deeply matt, chalky wall paint with about a 2% sheen — that velvety, light-eating depth that makes colours like Hague Blue or Mole's Breath look so good. The catch: it's delicate. Scuff it or scrub it and it'll mark or burnish. Brilliant for adult bedrooms, sitting rooms and dining rooms where it won't take a battering. Not for hallways with kids and dogs.
Modern Emulsion is the workhorse. Higher sheen (around 7%), acrylic-based, fully washable and far more durable. This is what you want in kitchens, bathrooms, stairwells, kids' rooms — anywhere that gets touched, splashed or scrubbed. You lose a touch of that flat chalkiness, but on a busy wall it's worth it. If you love a colour like Cornforth White in a hallway, use Modern, not Estate.
Dead Flat is the dark horse. It's a near-zero-sheen finish (about 2%, like Estate's matt look) but it's tough and — crucially — it goes on woodwork as well as walls. So if you want skirting, doors and walls all in the same dead-matt colour for that immersive, sheen-free room, Dead Flat is your only F&B option. It's the trade favourite for a reason. It does need a clean, properly primed surface to look its best, especially on trim.
The one people forget about: Estate Eggshell is a separate finish for woodwork with a low sheen — don't confuse it with the three above.
Practical rule: matt and low-wear room, Estate. Wipeable and high-wear, Modern. Same dead-matt colour on walls and trim, Dead Flat. Sort your prep either way — F&B finishes reward good walls and punish dodgy ones.