Good question. Let me explain in the following way.
1. “Dhamma” means “to bear.” That is the most encompassing definition of “dhamma.”
– Most times, this idea is expressed by the word “dhammā” (with a long “a” at the end). For example, “Ye dhammā hetuppabhavā” refers to how everything in this world arises due to dhammā (kammic energies) created by the six hetus (lobha, dosa, moha, alobha, adosa, amoha).
– The mind generates such kammic energies (dhammā) via the generation of abhisankhara/kamma vinnana/namarupa generation in Paticca Samuppada. With the complete cessation of avijja that process stops at the Arahant stage.
2. Until the above process is understood at the Sotapanna Anugami stage (and fully understood at the Arahant stage), all minds engage in creating “dhammā”. That leads to rebirths when those kammic energies bring new “bhava/jati”.
– Within those new bhava/jati, “dhammā generation” continues.
– Thus it is a cyclic process: kamma generation leads to future births. Within each birth, there is more kamma generated.
– This “cycle” is “cakka” in Pali. Thus the term, “Dhamma Cakka” or the “wheel of Dhamma”.
3. Now, this cycle can be broken only by comprehending “Buddha Dhamma”.
– “Buddha” comes from “bhava uddha” or “stopping new bhava”. Thus, “Dhamma” in “Buddha Dhamma” act in the opposite way “normal dhamma” which leads to rebirth.
4. In his first sutta, dhammacakkappavattana sutta” the Buddha explained how that “cyclic process” sustains the rebirth process filled with unimaginable suffering.
– Here, “dhammacakkappavattana” = “dhamma” “cakka” “pavattana” where the last term means “keep in motion”.
– It has a double meaning. By understanding that process, one can overcome it and be free of it.
– P.S. The cyclic process of samsara is stated in the “Paṭhamabodhi Sutta (Ud 1.1)“. That is the “Forward Paticca Samuppada.’ The stopping of that process is with the “Reverse Paticca Samuppada” stated in the next sutta: “Dutiyabodhi Sutta (Ud 1.2)“ Those are the first two sutta in the Udana section of the Tipitaka.
5. Finally, “cakka” is not to be confused with “cakkhu“.
– Cakkhu means to see.
– “Dhamma cakkhu” is a “special seeing with wisdom (with Buddha Dhamma) about how that samsaric cyclic process takes place (and to overcome it).
– Thus, the Buddha refers to “dhamma cakkhum udapadi” or the “arising of wisdom eye” upon attaining the Buddhahood in the same Dhammacakkappavattana Sutta.