One of the side effects of the great expansion of printed materials which had occurred in the 15th and 16th centuries was the standardization of language used by those involved in technical fields. Engineers, naturalists and mathematicians, over the course of many generations, began to communicate in terms which only they could understand. So, it didn't matter if, say, two astronomers were as separated by distance or parlance as far as Paris and Pisa, the technical aspects of their correspondence could be understood. The characteristically ubiquitous language of scientific disciplines has now been carried to its logical conclusion. Today, all biologists, for instance, use the generic and specific binomial to describe any organism (e.g. Felis sylvestris, rather than, the housecat).
The commonality of language helps to prevent a confusion of terms, which would be the inevitable consequence of using colloquial terms for objects or phenomena. Imagine the confusion! A panther could refer to a leopard, but it is also the common name for the North American puma and the South American jaguar. The difficulty would become even more acute if we attempted to describe the amazing molecular machines within our own bodies. What if the enzymes conducting the numerous functions on our DNA had only non-descriptive names, like the DNA Un-Zipping Molecule. Biochemistry wouldn't have gotten anywhere.
Kidding aside, there exists a group of individuals who like to believe they're involved in science, but have difficulty speaking the language of science. Creationists can be frequently identified by their inability to use terms in the proper context, or even give a proper definition. Take the word evolution, which has been so reviled by the Biblical literalists for over a 150 years. Ask almost any creationist, and you're likely to receive many answers, from the beginning of the universe, to the origin of life, to the even less thoughtful "people coming from monkeys". Evolution has even been described as the religion of atheism. For a biologist, evolution means none of those things. It merely means the change in populations of organisms over time. By extension, the theory of evolution is a framework to explain the emergence of new populations, also known biodiversity.
There is also a reason for this inability to use terms properly. Once a creationist is forced to define a term, then the meaning must be defended. Nebulous terms are much more easily guarded, and this allows these dishonest hucksters to shift the goalposts so they can pretend to always be correct. This is especially useful in a "debate" which has nothing to do with science, and everything to do with applying social and political pressure.
Here's another fun example of an undefined definition. The frequently used word "kind" to describe an organism or group of organisms. However, if a creationist is asked to define a "kind", he'll usually be elusive. If, perhaps, one was describing my cat, could she be of the "cat kind"? But given the diversity of felids, how meaningful is this term? If a sand cat or ocelot are "cat kinds", are lions as well? Or are lions of the "panther kind"? The problem with this definition is that cats alone can be grouped into steadily broader and more inclusive groups until all life on Earth could be included. Watch what happens to the classification of my cat into a "kind", and try to find a position in which she could not be included.
1. The house cat kind.
2. The feline kind, which are generally smaller cats and include the cheetahs and cougars.
3. The felid kind, which would also include panthers.
4. The feliform kind, which would also include hyenas and meerkats.
5. The carnivore kind, which add caniforms such as bears, dogs and sea lions..
6. The mammal kind, characterized by specialized glands for producing milk, which include wallabies and whales.
7. The tetrapod kind, which are all land dwelling vertebrates, from geckos to geese.
8. The vertebrate kind, animals with a bony spinal column, such as halibut and hagfish.
9. The deuterostome kind, which are animals in which the embryo forms the gut from the anus first. Starfish and sea squirts are also deuterostomes.
10. The bilaterate kind, which are all animals which are symmetrically divided from stem to stern, like earthworms and earwigs.
11. The eumetazoan kind, animals made of tissues, such as man o' war and myxozoans.
12. The metazoan kind, all animals, which are any multicellular organisms which must ingest other organisms to gain energy. This kind would include porifera and placazoans.
13. The opisthokont kind, organisms which produce sperm propelling themselves with a posterior flagellum. This group includes mushrooms and molds.
14. The eukaryote kind, which are organisms with a membrane protecting their genetic material, called the nucleus. The kind which adds magnolia and malaria.
15. The biotic kind, life on Earth, from bacteria to bactrian camels.
There are many other characteristics that could be mentioned which would add more exquisite detail, but a few thoughts emerge even from this cursory glance. First, that in trying to define "kind", the creationist must expand into an ever increasing hierarchy which eventually includes anything alive. Second, by demonstrating this hierarchy of "kinds", common ancestry is also demonstrated.
Finally, the taxonomic levels listed here would have been meaningless unless, of course, biologists had not defined them first.