"Area" is an ambiguous term when referring to three-dimensional shapes. "Area" could refer to the following:
For a regular tetrahedron, the surface area is as follows:
\(SA=a\sqrt{3}\)
The area of a face for a regular tetrahedron is as follows:
\(A_{\text{face}}=\frac{a^2\sqrt{3}}{4}\)
In both cases, "a" represents the length from one vertex to another.