Pasta Liscia is a term meaning “smooth pasta.”
You will see it used in context of pastas that may have either smooth or “rough” surfaces.
It’s generally not used to describe a pasta that is always just presumed to be smooth, such as macaroni.
You will also see the “liscia” spelled with the “ia” dropped and an “e” or an “i” tacked instead on the end when it is used in combination with a plural word. e.g. penne lisce.