The AFTE Glossary 5th Edition currently identifies a striation as:

Contour variations, generally microscopic, on the surface of an object caused by a combination of
force and motion where the motion is approximately parallel to the plane being marked. These
marks can contain CLASS and/or INDIVIDUAL CHARACTERISTICS.

Does anyone have a more detailed description that they give in reference to "contour variations" when asked in court to explain what is meant by contour variations in regards to a striation?

Current research  that describes the various understanding of a striation in regards to diverse explanations of what a striation is (i.e. length, width, depth, and microscopic appearance) could assist in a more detailed and direct response should this term ever be questioned in a court of law.

I usually discuss striations when I am explaining the individual characteristics of a barrel.  I explain the purpose of rifling and then go on to explain how the tools leave randomly placed individual characteristics in the form of nicks, burrs, and cuts in the barrel.  I then explain how the bullet travels down the barrel and that it is not only engraved by the rifling, it is also marked by the barrel's individual characteristics which form a pattern of striations, or scratch marks that a firearms examiner uses to determine if a bullet was, or was not, fired from that barrel.  This has worked for eleven years so far but it could be that the jury is asleep by that point.

TK