Simplify the following text for a Grade 4 native English-speaking person.
Original: Others apply acute to pain that lasts less than 30 days , chronic to pain of more than six months duration , and subacute to pain that lasts from one to six months . A popular alternative definition of chronic pain , involving no arbitrarily fixed durations is `` pain that extends beyond the expected period of healing . ''
Simplified: Chronic means the pain lasts a long time .