Shilling is a form of promotion that does not disclose it is promotion or having any indication that it is promotion.
In our space that can be seen a few ways, the biggest of which is, some supliers in the industy will send free product, unanounced to the public product to someone, specificly with a expectation of direct promotion from the person.
There is often a blury line in the skate scene surrounding this with riders who are "flowed" gear, which may make is seem like a brand etc is more popular/well liked than it is.
To help un-blur the lines with this site usage we require those in the industry to disclose their status.