Characters, especially females, wear armor that's unconvincingly sparse in body coverage and protection, much like a bikini, or is thin and form-fitting like a bodysuit.
Alternate name: Bikini armor
The first video game about Unconvincing armor was released in 1982.
Form-fitting bodysuit/unitard/catsuit-style armor may also be considered part of this.
Especially egregious are the games where same armor gives full (or at least fuller) body coverage for male characters but cover female characters only minimally (something resembling lingerie rather than armor).
A classic example from Valis X:
See also: combat stilettos