It means particles that appear on the hardened steel. It is not the same thing that the particles on the hamon (usually it is called just "Nie"). Hamon particles are "discrete martensite".
Jinie may be some kind of steel crystal, but I don't know as metallurgy. It looks like very fine grains made of wet sands. In other words, well hardened steel is a mass of these particles, or a mass of JINIE.
Some JINIE particles look small, and some look bigger. Some are dense, and some are sparse. The appearance is beautiful and interesting. And to study JINIE particles is important to appreciate the blade. Now, we translate "JINIE" to "steel particles".

In some cases, the steel particles array makes a formation like wood grain. We call it CHIKEI.
 
 
CHIKEI
It is one form of JINIE.
Sometimes steel particles run to make an array. Some look like a wood grain pattern, and some run irregularly like a web pattern. We call such an appearance "CHIKEI".
CHIKEI is not the meaning of a layer pattern. Some CHIKEI appear along the layer pattern, and some are across the layer pattern. A good steel has a CHIKEI that is free from the layer pattern (across the layer pattern).

We hope you can see the chikei runs like web.

 
For examples;
Some of the good quality Hosho blades in Yamato province have a straight layer pattern, but the CHIKEI appears like a small wood grain pattern.
The steel of Shintogo Kunimitsu's tanto has full of CHIKEI that is along the small wood grain layer pattern. And his student Masamune's steel has emphatic CHIKEI that appears along the large layer pattern.
In fact, we don't appreciate a chikei along the layer pattern too much. Sometimes it is an appearance come from mix steel folding, either intentionally or natural from uneven quality material.
 
Examples;
A steel of a Shintogo Knimitsu tanto.

 
A steel of an Awataguchi Kuniyoshi tanto. It is full of fine chikei.

 
The next two photos are the same steel of modern blade, but in different polishing. Please see the areas we marked. The first polish brings the chikei (grain of steel particles), and the second polish brings the layer pattern (straight pattern grain).

Another kind of chikei that runs along the layer pattern. It is a black shining steel among the layer. It doesn't tend to be called chiki, but recently such an apearance also be called chikei in the context of Art sword.


(=> Is the grain changed by re-polishing?)
 
One more example
Yukihira in Bungo province in 12th century is famous for YAKIOTOSHI hamon. Yakiotoshi is a hamon that starts at a distance from the tang.
On his blade, at the part below the mizukage, the steel has large flowing wood grain pattern. And the upper part of the mizukage is a very small fine wood grain pattern. But, by careful study, the layer pattern continues the entire length of the blade.
The grain below the mizukage is an appears of the layer pattern, and the grain of upper part is formed by steel particles.

 
CHIKEI is one of the most interesting appearances of the steel of a Japanese blade. To study CHIKEI is important to appreciate the quality of steel.
 
-Another way to use the word "CHIKEI"-
In some cases of mix folded steel, there is a CHIKEI like layer pattern without JINIE effect. Sometimes it is also called CHIKEI, but such grain is not a criterion of steel quality. CHIKEI has to be an array of steel particles.
In the meaning of Art Sword, a running bright pattern in steel is called Chikei anyhow.
 
An example of chikei-like pattern in Shin-shinto blade. It is made of mixing with hard steel and mild steel. Such a chikei is designed by the smith as an art.

 
JIFU
It is also one form of JINIE.
JIFU is an area that is made of dense CHIKEI, in other word the tightest form of steel particles. It is distinguished from the steel surface. It has a clear border and deeper colour than the other part. Of course it appears free from the layer pattern. It is not bordered with a layer pattern.
The transformation steps of steel particles is: JINIE => CHIKEI => JIFU

 
JIFU may appear only on good KOTO blades, but it still is rare. We appreciate JIFU very much.
 
-Another way to use the word "JIFU"-
Sometimes a distinguishable spot that comes from different steel as material, is also called JIFU by some people. But this type is not a criterion of good quality. It is just an different steel. Such a spot is shaped with the layer pattern. It does not come from the hardening effect.
In the meaning of Art Sword, a spotted appearance what is different from the other surface is called Jifu, anyhow. So the word "Jifu" could be used for a situation of core steel appearing.
 
An example of spotted steel (Namazu-hada, Sumi-hada, Sumi-gane) in Aoe blade. It could be called Jifu by some people.