The basic answer to this confusion is that classifying a wood as either soft or hard is entirely dependent on the seeds that are produced by the tree where it comes from. If the seeds of the tree have some sort of covering when they fall to the ground, be it in a form of a fruit or shell, then the wood of that particular tree will be classified as hardwood. On the other hand, if the tree will produce seeds which are simply left to the Earth’s elements when they fall to the ground, then the wood that is harvested from the tree is classified as softwood. The technical term referring to a tree which produces seeds with any sort of covering is called the gymnosperm. This word is derived from Ancient Greek which when literally translated means naked seed.
With regards to trees that produce seeds which are covered, the technical term for them is angiosperm which is a word that is derived from Ancient Greek that when roughly translated would mean seeds contained in a vessel. The angiosperms include any type of tree which produces fruit as well as those trees that produce seeds that are protected by some shell like the acorn. The term angiosperm was actually first coined back in 1690 by Paul Hermann who is a German botanist. It was a way of classifying the different members of the plant kingdom by what they had in common- seeds.
Although the terms softwood and hardwood are not really related to the relative toughness of a certain piece of wood, for the most part, hardwoods are typically much harder compared to softwoods. This then leaves one very obvious question as to how exactly one classifies how hard a certain piece of wood. The most common way is using a Janka Hardness Test. This has been the industry standard since the 1906. This technique involves measuring the average amount of force that it applied to a certain type of wood. It can also be determined through distinguished side hardness and end hardness. The Janka test is authored by Gabriel Janka who came up with the idea after asked by the DA to find a scientific and objective way in measuring the hardness of a certain piece of lumber.
Now that you know the difference, you already have the idea if you should go to a hardwood supplier or softwood supplier when creating or building something.