"Tatoos," properly spelled "tattoos," are permanent markings made by inserting ink under the skin. The word in English is thought to come from a Polynesian language, and to have been brought to Europe by Captain Cook and his sailors.
The practice has, however, been known in many parts of the world, with the first known one being on Oetzi the iceman, who died about 5,300 years ago. A related practice, scarification, was more commonly practiced in Africa.
Bloggers writing about tattoos are most commonly commenting on their own plans to get a tattoo, admiring the tattoos of others, or thinking about how to remove them. Or they might be making the point that tattoos can be for all ages.