Professional appears on consumer telescope boxes and in listings for instruments costing a few hundred pounds, and it means nothing there. It does mean something in astronomy, and the gap between the two uses is worth understanding before spending money on the word.
What a professional instrument actually is
Research equipment: apertures measured in metres, permanent buildings, cooled scientific detectors rather than eyepieces at the focus, and observing time allocated by committee against a proposal. None of it is for sale, and no consumer instrument is one of these in any sense.
What the word means on a box
Usually nothing, and occasionally a genuine mid-range instrument. It is a marketing adjective in the same family as high powered, and like that phrase it is more common on the products least able to justify it. Read the aperture instead, which is a fact rather than a claim.
What a serious amateur actually buys
Large dobsonians, premium apochromatic refractors, high accuracy mounts and cooled cameras, in various combinations. These are excellent instruments and some cost as much as a car, and none of them is professional equipment. The distinction is not snobbery: it is about what the instrument was designed to do.
Where the money genuinely goes at the top of the amateur market
Mount accuracy, optical figure and field correction across a large sensor. Those three account for most of the price difference between a good instrument and an extraordinary one, and none of them is visible in a photograph of the telescope.
Questions people ask about telescope
What is a professional telescope?
Research equipment at an observatory, with apertures in metres and time allocated by committee. Not a consumer category at all.
Can I buy a professional telescope?
No. What you can buy is excellent amateur equipment, some of it very expensive, which is a different thing designed for a different purpose.
Is a professional telescope better?
For research, by an enormous margin. For a person standing in a garden, an instrument they can carry and use is better in every way that matters.