What does the term 'stock photo' mean?

The concept of stock photography
Anyone who makes posters, writes a blog, or edits newspaper articles may have come across the term 'stock photo' and is aware of the meaning of the term. If you’re looking for photos for an ad on Facebook, you’re probably going to be taken to a free stock photography site because a lot of marketers recommend it.
So what does stock photo mean?
The phrase refers to millions of photos that are stored by specialized agencies / companies (now online) for you to choose from. The stock never runs out, as a photo can be sold in unlimited quantities by the company because it does not sell the image itself, but the right to use it. Rarely, a buyer buys an exclusive right of use, i.e. the image has to be removed from the seller’s list of photos. In this case, based on an individual agreement, the picture can be sold for a rather high amount of money.
When is it worth buying stock photos?
The answer is obvious: if you can't take your own picture. A daily newspaper cannot always provide its own photos to its articles, so it is forced to choose from the offerings of stock photography sites. For a themed calendar, it’s easier to collect the right images from a stock photo site than to travel all through the country.
How much is a stock photo?
Basically, the stock photo business is developing in two directions. Free or paid.
The free platforms make a significant amount of good quality photos available, so if you don’t want to spend on something like this, this option seems like a good choice. However, I suggest thinking about it, if a photographer offers his or her expertise and time in the form of a stock photo, does he or she deserve some benefit in return? If your answer is yes, he/she deserves something in return, please choose the next option.
The number of websites offering paid options is significantly higher and the number of images they sell is also much more. There are cheap (microstock) sites and there are more expensive (midstock or macrostock) companies.
Traditional stock agencies sell their pictures more expensive, but you can find plenty of unique photos in their portfolio that can't be found elsewhere. While e.g. Shutterstock or Adobe Stock microstock agencies limit the subject and content of photos that can be uploaded to their website, Alamy (midstock) does not examine photos at all for content, they only do quality control. So on the Alamy stock photo site you will find a lot of unique photos, albeit at a higher price than at their microstock counterparts.
The downside to microstock photos can be that you may come across the same photo many times on the Internet, as cheap stock photos are bought many times. This applies to free stock photos, too.