Words are important they are often short-hand for complex ideas. Sadly a shared vocabulary does not represent a shared understanding. This is the frequent source of humour but also misunderstandings. If an American for example, talks about changing his pants an Englishman understands him to be changing his underwear while the American simply means changing his trousers.
When it comes to Biology specific words have specific meanings. Sadly we use those words with varying degrees of accuracy. The context usually determines the meaning but for the sake of clarity I have endeavoured to provide a glossary of terms.
Gene - frequently used to mean the genetic code for a charqacteristic or trait. More specifically it means a specific location on a chromosome where the DNA codes for a specific protein.
Allele- this uses the tighter definition of a gene and represents a variant found at that location. In sweet peas for example there is a specific location for flower colour. Red and white alleles exist for the same gene location.
Variable species - this term is not well known in Biology but it describes an organism which can alter it's morphology to fit in with the environment. The swarming locust and the solitary locust are genetically identical for example. When the population of the solitary locust increases, it triggers a change in morphology and behaviour. What was basically an individualistic grasshopper, now becomes a gregarious, destructive swarm. The brown trout can become migratory and becomes the seatrout. Should it become landlocked it reverts to being a brown trout - with no change in its genetics.
Micro-evolution - this basically describes the observed effects of natural selection in speciation. It does not describe the origins of new genetic information. An insect eating finch with a fine bill may develop a heavier bill and switch to tough seeds. Most creationists I know would accept micro-evolution as a proven fact (within a creationist framework).
Macro-evolution - this describes the change of one genus into another. It represents a scale of change much greater than the speciation observed in micro-evolution. It is an extrapolation from micro-evolution but does not have the observable evidence that speciation does. A finch has not been observed become a hawk with increased visual acuity and the development of talons to name but two changes. Most creationists I know would not accept macro-evolution as a proven fact.
Species - It took a few years to realise that there are two definitions of a species. Biological species -the one we are most familiar with is that a fertile breeding population of organisms represents a species. This test of fertile interbreeding however can be ignored when inconvenient. The Ruddy Duck interbreeds with the White Headed Duck in Spain and the offspring are fertile. This means that they are the same species? Not according to the RSPB who have instigated a cull to protect the endangered White Headed Duck.
Fossil species - obviously the test of interbreeding is impossible to carry out. Instead the overall morphology is the guide: if it looks different then it's a different species. Not so long ago a small species of T-rex were reexamined. The bones were found to be juvenile bones and the small species had to be re-classified as simply juveniles of the larger species (adults).
Genetic death - this is a peculiar term since it describes the removal of a gene from the gene pool using a term normally associated with the demise of an individual organism.