Contrary to what the AC said subwavelength is not technobable. I am a lithographer. Its basically referring to being able to resolve images smaller than the wavelengths of light you are doing the imaging with. You cannot see a virus through a microscope because the visible light emitted from it has a wavelength that is too large to allow enough diffraction orders into the lens to allow it to resolve any valid features at your eye. This is the Rayleigh resolution criterion in action. In practical lithography cases we add in a K1 factor to Rayleigh's equation to quantify how difficult an imaging case is for a given wavelength and NA.
Subwavelength imaging has been around in semiconductor processing for decades with people using tricks such as off-axis illumination and phase shifting masks to allow a 365nm light source to print 200nm features or a 193nm light source to print 45nm features. If you have used a computer in the last 20 years odds are most of the critical layers were imaged using subwavelength imaging.