There's a Russian word "джинса" (here's an article in Russian if one wonders) for articles that feel like ads (and most probably are de-facto hidden ads indeed) but not officially marked as such. My question is, apart from the term "hidden ad", is there a specific English term for this?
A newspaper or magazine article, which is written in the form of an editorial article, but is actually promoting a product is often called an advertorial, but some marketing/advertising people prefer the term "Native Advertising" and attempt to create a distinction between this and advertorials, though to me the distinction is vague at best.
Often magazines will have ads that are created by third-parties which are deliberately designed to resemble the appearance of a legitimate news article, by using layout and fonts similar to the magazine's own. Often they are required to provide some sort of disclaimer that it's actually an ad, but the disclaimer is generally small and easily missed. Some magazines actually cooperate in creating such advertising, even doing the layout. Sometimes an actual article or editorial is written by a staff writer, but simply contains promotional content. This is very common with local area magazines or TV news programs.
If I read your question correctly, you are talking about print or online media that features the written word, because you've used the term "article".
I worked in advertising for more than 25 years. "Infomercial" is used for broadcast media -- audio or video.
The term most often used for media featuring the written word is "advertorial". For example, special sections in newspapers that are sponsored by corporations or regional tourism boards are advertorials.
Sponsored Content is often used for a news story partly or wholly paid for by the seller. The following promotes the use of sponsored content. https://www.activecampaign.com/blog/sponsored-content. There seems to be no single general word, only phrases.
Sponsored Content: What You Need to Know (and 9 Examples!) SEPTEMBER 30, 2019
. . . These phrases are indicators of sponsored content. They mean that a brand has spent some money to get some content in front of you.
If the article is presented as being from the public or expressing a populist opinion, you might also hear the term astroturf or astroturfing applied. These terms are sometimes capitalized, as AstroTurf is a brand name of artifical grass (as a play on the term "grassroots" to mean a local or populist movement/agenda).
Wikipedia's article on astroturfing describes it as "masking the sponsors":
Astroturfing is the practice of masking the sponsors of a message or organization (e.g., political, advertising, religious or public relations) to make it appear as though it originates from and is supported by grassroots participants.
From Wiktionary's page on astroturf (adj):
Of a group created by a larger organisation (especially a corporation or political party), but presenting itself as a grassroots organisation.
For reference, from Wiktionary's page on grassroots (adj):
Of, or relating to people or society at the local level, particularly in politics, social movements, etc.; of the grass roots.
In this sense "astroturfing" is the generic term that can be applied to legal and illegal advertising content that is not clearly marked, where "advertorial" or "sponsored content" are labels generally applied by the publishers to disclose that sponsorship and avoid legal repercussions.
We have the term infomercial (coined as a combination of "information" and "commercial").
An advertising film which promotes a product in an informative and supposedly objective style.
I like the term "Checkbook Journalism" or "Prostituted Journalism". Journalism should be about the truth. Most pieces are now just the opinion of whoever is paying the journalist. Pay can be in the from of advertising or a paycheck. Sad but true, unless we are independently wealthy, but we have to serve somebody. Being your own man as Kipling said is a hard business. So if you can buy a CNN or a journalist you can have your opinion presented as the "Truth". The rest of us will be limited in our own sources for the truth.
- Subliminal advertising tries to influence people without them being aware of it, for example by showing messages for such a short time that people read them without realizing that they have done so. CD
subliminal - not recognized or understood by the conscious mind, but still having an influence on it. CD
- This newspaper was full of subliminal messages about the new product
- His speech was full of subliminal prejudice, which will surely influence some voters.
Dictionary.com defines subliminal message as a technique used in marKeting and other media to influence people without their being aware of what the messenger is doing. This may involve the use of split second flashes of text, hidden images, or subtle cues that affect the audience at a level below conscious awareness.