A zit and a pimple are the same thing. One word is casual, the other is slightly less casual. There is no medical difference, and no doctor will treat them differently.
A boil is not the same thing. A pimple is a blocked pore. A boil is a bacterial infection of a hair follicle, and it goes deeper, hurts more, and lasts longer.
The quick version: a pimple comes up in a day or two, peaks, and is gone within a week. A boil keeps growing for several days, becomes genuinely painful, and gets big enough that you stop wanting to touch it.
Bacteria — usually Staphylococcus aureus — get into a follicle and your body walls them off. It is a small abscess.
Oil and dead skin plug the opening. Normal skin bacteria multiply in the trapped oil and the area gets inflamed.
Keeps growing over several days.
A few millimetres, and it stops growing quickly.
Throbs on its own, not just when pressed. Often too tender to lie on.
Sore if you press it. Easy to forget about otherwise.
Builds for days, comes to a head, drains, then heals.
Back of the neck, armpits, groin, buttocks, thighs, waistband line.
Face, chest, upper back, shoulders.
A large boil can come with fever or feeling generally run down.
A warm damp cloth for ten minutes, three or four times a day, helps it come to a head and drain on its own. If it keeps growing, a clinician numbs it and drains it — that gives immediate relief.
Benzoyl peroxide or salicylic acid on the area. It will resolve. Picking is what turns a three-day spot into a three-month mark.
Draining is the main treatment. Antibiotics are added for larger boils, spreading redness, fever, or certain locations.
Not for an ordinary spot.
Deeper damage, so more likely to leave a mark.


No. Same thing, two words. "Zit" is informal, "pimple" is the everyday word, and the medical terms describe the specific type:
That last group is the one that matters. Deep painful lumps that last weeks are cystic acne, and they need prescription treatment. Waiting them out is how people end up with permanent scars.
Repeated boils in the armpits, groin, buttocks, or under the breasts are often not boils at all. That pattern — the same few areas, over and over, sometimes with tunnels or scarring between them — is hidradenitis suppurativa.
It is a long-term inflammatory condition, not an infection, so courses of antibiotics keep helping a little and never fixing it. It is very commonly mistaken for bad luck with boils for years before it is named. It is treatable, and getting the right name is the whole first step.
If you have had more than two or three "boils" in a skin fold, mention that pattern specifically to a doctor.
With a pimple, squeezing pushes the contents deeper into the skin, which makes the inflammation worse and is the main reason spots leave brown marks and dents.
With a boil, squeezing can push bacteria further in, and can spread the infection to the surrounding skin.
Neither one has anything useful you can get out at home.