The IUPAC name of neopentane is:

Neopentane has the structure where a central carbon is attached to four methyl groups.
$$\text{C}({\text{CH}}_3{)}_4$$
The longest continuous carbon chain consists of $3$ carbon atoms (propane). Two methyl groups are attached to the second carbon atom. Therefore, the IUPAC name is $2,2$ -dimethylpropane.