Definition:Perfect Field/Definition 1

Definition
Let $F$ be a field.

$F$ is a perfect field  $F$ has no inseparable extensions.

Also see

 * Equivalence of Definitions of Perfect Field
 * Frobenius Endomorphism on Field is Injective
 * Definition:Separably Closed Field, a field with no separable extensions

Examples

 * Galois Field is Perfect
 * Algebraically Closed Field is Perfect