I'm guessing there may be a translation issue here, but are you asking about studs (safety and solid) on Minifigure heads? If so, a safety stud has three small holes (to allow air to pass through should a child accidentally swallow one) whereas a solid one does not (and looks like a normal LEGO stud). There is a third version, hollow stud, which is not open but the logo is sunk into the stud.
If this is not what you're asking then apologies, and someone else may be able to help.
What are we not doing for our children ..., world class. Fortunately, the first time I grabbed a head, I saw your hint. Thank you very much for the answer.
There is also a fourth one that can be found on translucent colored heads from the past year or so. Very similar to Blocked Open but instead has small bar going down the middle of the stud making two holes. Brickowl so far does not have them, but on other sites they are called vented.
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If this is not what you're asking then apologies, and someone else may be able to help.