Spotting is a very small amount of blood, typically just a few drops.
Spotting is characterized by light bleeding, typically identifiable as a few drops of blood on your underwear. It's so minimal that it wouldn't be enough to even cover a panty liner. This distinguishes it from heavier bleeding, which necessitates the use of a panty liner or pad to prevent staining clothes and underwear. In essence, spotting is lighter than a light period flow.