Stealth advertising is marketing your product to the target audience without them realizing you are doing so. Strategies may involve product placement and undercover marketing.
Stealth marketing is done by companies to make people comfortable with their product idea. Immediate sale generation is not their main aim. They want to make their customers future ready for their product.
It is cost effective but stealth marketing is often considered non-ethical.
An example of stealth marketing is when their is a TV commercial being run on TV and some other brands poster is slyly added in background.