The Merriam-Webster dictionary defines a poison in broad terms (noun. A substance that through its chemical action usually kills, injures, or impairs an organism) and venom as (noun. A toxic substance produced by some animals (such as snakes, scorpions, or bees) that is injected into prey or an enemy chiefly by biting or stinging and has an injurious or lethal effect). These definitions have been in common usage, however, they don't adequately encapsulate the intricacies and variation observed within biological toxins.
Recently, scientists have proposed more rigorous definitions (see 2014. Nelson, et al. Biological Reviews 2014(89): 450-465.) of toxic biological secretions to eliminate the rampant inconsistency and ambiguity while facilitating better communication for such a medically important topic.
The standards and stringency of clarity by which scientists discuss poisons/venoms and the organisms that produce them, should not be held to the general public. The layperson referring to a "poisonous snake" is not wrong and the message is clear.

The study of biologically produced toxins is toxinology. Toxinologists have adopted the mechanism of delivery and transfer to delineate a biological toxin as a poison, venom, or toxungen.

Poison — An exposure via self-infliction (whether on purpose or by accident). It doesn’t have to be just ingestion-inhalation as dermal contact is common for this as well. Licking an American Toad or Pickerel Frog is a poisonous exposure. Poisonous exposures are typically thought of as “passive”. A unique area of poisoning would be someone injecting themselves with snake venom (i.e. to produce antibodies/immunity) and whether it should be considered a poisonous (not animal mediated) or venomous (injection) injury.
Examples of poisonous herps in Kansas include True Toads (Anaxyrus spp.), Cope's/Gray Treefrog (Hyla chrysoscelis/versicolor), and Pickerel Frog (Lithobates palustris).

Venom — Where the organism that produces the toxin(s) is the one delivering said toxin to the person-historically this has been via a bite or other means of mechanical injury or wound (injection typically). Venomous exposure is typically thought of as “active”, however, there are some exceptions with some species of caterpillars that always have erect spines to result in envenomation if touched and don’t have to actively do anything different even in reflex to deliver the toxin.
Examples of venomous herps in Kansas are five species of the family Dipsadidae (harmless rear-fanged snakes; Carphophis vermis, Diadophis punctatus, Heterodon spp., and Hypsiglena jani), several species of the family Natricidae (e.g. Thamnophis spp. [Gartersnakes]), several species of the family Colubridae (e.g. Tantilla spp. [Crowned Snakes]), and five medically significant species of the family Crotalidae (pit-vipers) (Agkistrodon spp., Crotalus spp. and Sistrurus tergeminus).

Toxungen — There is a specific term for topically applied venom such as the case with spitting cobras where it does not cause a mechanical injury but is actively applied. The Texas Horned Lizard (Phrynosoma cornutum) is an example of a possible toxungenous Kansas herp species.

The overarching definition for all of these falls under biological toxins. Most biological toxins are a complex mixture of several toxins, each with unique physical and pathological properties. A species may be both poisonous and venomous (e.g. Rhabdophis of Southeast Asia). But you also have many venomous snakes that are not poisonous because people can eat them with no issues. Sometimes with large amounts of ingested venom, you can have GI effects or an ulcer develop, but our stomach acids and associated proteases can denature many of the enzymes found in venoms.

Dangerously vs. Harmlessly Venomous — Dangerously venomous herps are a threat to human life or limb and bites from these snakes should always be considered medically significant. Harmlessly venomous herps use their venom to subdue prey but are typically not dangerous to humans because a) they have an ineffective venom delivery mechanism, b) their mouths are too small to gain purchase, and c) their venom is not adapted for causing physiological damage to mammals. The distinction is largely based on the general function of the venom itself, however, humans may react differently to any envenomation based on their unique physiology. It is a good precaution to immediately monitor any suspected snakebite.

Venomous Snakebite — If you happen to be bitten by a venomous snake follow these steps. The immediate pain and swelling should confirm that you have been envenomated, however, if you have any questions about it, assume that you have been.

• Seek medical attention as soon as possible (dial 911 or call local Emergency Medical Services EMS). Do not wait for the person to look or feel sick.
• If you are alone, get to a place where you can call 911, be seen, or otherwise attract attention.
• Keep calm.
• Call The University of Kansas Hospital Poison Control Center (KU-PCC) at 1-800-222-1222. The Poison Control Center will advise you on the correct treatment and help you determine whether you need to go to a hospital or a doctor’s office and what care they should provide. There is a broad range of experience among care facilities in treating venomous snakebites, the KU-PCC will bring a toxinologist into every snakebite call.
• Antivenom is the treatment for serious snake envenomation. The sooner antivenom can be started the sooner irreversible damage from venom can be stopped.
• Driving oneself to the hospital is not advised because people with snakebites can become dizzy or pass out.
• Apply first aid while waiting for EMS personnel to get you to the hospital.
• Lay or sit down with the bite in a neutral position of comfort.
• Remove rings and watches in anticipation of swelling.
• Wash the bite with soap and water.
• Cover the bite with a clean, dry dressing.
• Mark the leading edge of tenderness/swelling on the skin and write the time alongside it.
• DO NOT: try to collect the snake, apply a tourniquet, cut or suck on the bite, apply ice, drink alcohol, take painkillers or antihistamines, or any other activity not listed above.

* Thank you to Elizabeth Silver, (PhamD, DABAT) and Stephanie Baines, (MA, CHES) at The University of Kansas Health System, Poison Control Center for discussion and explanation.