Squib

From Hpwiki

A squib is a person without magical power born to a witch and a wizard. This is the inverse of a Muggle-born wizard. Squibs are much rarer. Argus Filch and Arabella Figg are Squibs, as was Black family member Marius Black (who was disowned for being one).

There is some debate as to whether or not Squibs can see Dementors. Arabella Figg claims during Harry Potter's trial in Harry Potter and the Order of the Phoenix that she can, but it's possible she was just answering in the spur of the moment to defend herself.

Some Squibs have resulted to using Kwikspell, a "Correspondence Course in Beginners' Magic". This is introduced in Harry Potter and the Chamber of Secrets.