| context | $V$…$\ \mathcal F$-vector space |
| definiendum | $\mathrm{dim}(V)\equiv \mathrm{card}(B)$ |
| context | $B\in\mathrm{basis}(V)$ |
For finite vector spaces, the basis cardinality $\mathrm{dim}(V)$ is the only invariant w.r.t. vector space isomorphisms.
The Zero vector space has an empty base. Its vector space dimension is zero.
Wikipedia: Vector space