The human eye is unable to see objects that are less than 0.1 mm in size.
The objects that are too small to be seen through the naked eye are termed as microscopic. The resolution of an observer's eye determines the size of an object that can be visible. Microscopic objects include skin cells, bacteria, and algae. Microscopes are known to enlarge the apparent size of these objects. Due to the magnified image through a microscope, different points in an object can be seen distinctly.
Objects that are too tiny to be visible, without any visible aid (like microscope), through the naked eye, are termed microscopic.