There are various systems for cataloging pain, but for clarity of information, I will refer to the classification of the International Association for the Study of Pain (The International Association for the Study of Pain - IASP).
Generally, chronic pain, in terms of duration, is defined "opposite" of acute pain, so, voilà.
Remember, this juxtaposition is a bit deceiving: chronic pain is not a prolonged version of acute pain. It is quite another thing.
PAIN ACCORDING TO DURATION
Acute (inflammatory) pain
Acute pain has a limited duration in time and occurs after surgery, trauma or other conditions (infections, inflammation ...). Acute pain tends to decrease in most cases with normal and natural tissue repair, its duration often reflects the tissue involved (e.g. muscle injury vs bone fracture) and extensions of seven to over ninety days are common; however, it has a duration of less than three months. Acute pain acts as a warning to the body to seek help or to protect itself until the tissues are repaired, fulfilling an important biological function, avoiding the extent of the damage. Although it usually improves as the body heals, in some cases it may not happen, turning into chronic / persistent pain.
Chronic / persistent pain
Chronic pain remains beyond the time allowed for healing following surgery, trauma or other conditions (infections, inflammation ...). It can also exist without obvious lesions, ie chronic pain is not necessarily seen in a radiograph or in a scan (CT scan or resonance), in fact in the case of persistent pain, once excluded serious diseases such as cancer or neurological disorders, diagnostic investigations such as x-rays and scans (CT scan or resonance) are not recommended.
While chronic pain may be a symptom of another disease, it can be a disease in its own right.
If the pain lasts longer than the time needed for healing (generally this time is set at three months) it can be considered chronic.
Chronic pain is also defined as a persistent pain that "disturbs sleep and normal life, ceases to perform a protective function, while it degrades health and functional capacity". Thus, unlike acute pain, it has no adaptive function.
Conditions such as migraine, osteoporosis, arthritis and other musculoskeletal disorders (such as back pain, neck ...) are well known chronic diseases.
However, there are other chronic pain conditions that are not common or well known. They include conditions related to nervous pain, pelvic pain, abdominal pain, facial pain and persistent postoperative pain.
I explained to you what chronic pain is, but this explanation is not enough to understand it well. I'm still asking for a little more time. There is other information, perhaps even more important, that you need to have, which you will find on the page "Central Sensitization". Please read them. If you're tired, read in episodes. But you might find some explanations.
 The ACTTION – APS – AAPM Pain Taxonomy (AAAPT) Multidimensional Approach to Classifying Acute Pain Conditions
Kent ML, Tighe PJ, Belfer I, Brennan TJ, Bruehl S, Brummett CM, Buckenmaier CC 3rd, Buvanendran A, Cohen R, Desjardins P, Edwards D, Fillingim R, Gewandter J, Gordon DB, Hurley RW, Kehlet H, Loeser JD, Mackey S, McLean SA, Polomano R, Rahman S, Raja S, Rowbotham M, Suresh S, Schachtel B, Schreiber K, Schumacher M, Stacey B, Stanos S, Todd K, Turk DC, Weisman SJ, Wu C, Carr DB, Dworkin RH, Terman G. PubMed #28482098
 Turk, DC; Okifuji, A. (2001). "Pain terms and taxonomies". In Loeser, D .; Butler, SH; Chapman, JJ; Turk, DC Bonica's Management of Pain (3rd ed.).
 Chapman CR, Stillman M. Pathological pain. In: Kruger L, ed. Pain and Touch. 2nd ed. New York: Academic Press; 1996: 315-342.