THE ANSWER
They are two different regulatory claims. Permanent hair reduction means a lasting decrease in the number of hairs, with hair still present. Permanent hair removal means the treated follicle no longer produces hair. Laser is cleared for reduction. Electrolysis is recognised for removal. When any provider says "permanent", this is the question to ask.
Why
The distinction exists because the two treatments do measurably different things, and the terms were defined to keep marketing honest about which is which.
Reduction describes an outcome at the level of an area. After treatment there are fewer hairs than before, and that decrease persists. It does not claim any particular follicle has stopped permanently, and it does not claim the area is clear. It is a real and useful outcome. It is simply not the same as removal.
Removal describes an outcome at the level of a follicle. The growth cells have been destroyed and that follicle does not produce hair again.
In everyday marketing both get shortened to "permanent", which is where the confusion comes from. Someone told their laser course is permanent, who later finds hair in the treated area, has usually received exactly what was promised and not what they understood.
Worth noting that "permanent reduction" is a legitimate claim, not a trick. The problem is compression, not dishonesty.
Why does laser advertise "permanent" if only electrolysis is permanent?
Because "permanent hair reduction" is an accurate claim for laser and the word "permanent" is the part that survives into advertising. The full phrase is the honest one.
What does permanent reduction actually promise?
A lasting decrease in the number of hairs in a treated area. It does not promise the area will be clear, that any specific hair is gone forever, or that maintenance will not be needed.
What the evidence says
Laser devices for hair removal are cleared on the basis of permanent hair reduction. Electrolysis is recognised by the FDA and the American Medical Association as a permanent method of hair removal. These are established regulatory positions rather than competing marketing claims.
What to do next
When a provider says "permanent", ask which of the two they mean, and ask what you should expect to see in the treated area a year later. A good provider will answer plainly.
If the outcome you want is an area that stays clear rather than an area with less hair, that is removal. See electrolysis vs laser hair removal and gray, white and blonde hair removal.