Pseudo chiral centre
Carbon number 4 is a pseudo chiral center because its chirality depends on the chirality of the second and sixth carbons. For example, if the second carbon is S and the sixth carbon is R, then carbon number 4 can be r or s, but if the chirality of the second and sixth carbons are the same, then carbon number 4 is not the chiral center, because it doesn't have 4 different groups around itself.