Where the category begins and ends
The word 'hardshell' has no standards definition; it is category vocabulary that emerged to separate weather armour from everything else. In practice a jacket is treated as a hardshell when it combines a waterproof, windproof barrier fabric, fully sealed seams, and a feature set aimed at sustained exposure — an adjustable hood, protected zips, cuffs and hem that close against weather.
At the light end the category blurs into 'rain jacket': a packable 2.5-layer shell with taped seams is both. At the warm end it stops abruptly: the moment insulation is bonded in, you have an insulated waterproof jacket, not a hardshell. At the soft end it is bounded by softshells, which trade the waterproof barrier for stretch, breathability and comfort.
What a hardshell is for
The hardshell exists for conditions where being wet becomes a safety problem: sustained rain or wet snow, wind that strips heat, and exposure measured in hours. It is the outermost layer of a system, sized to fit over insulation, with a hood that works over a hat or helmet and pockets that sit clear of a pack's hip belt.
Check features on the exact garment: an adjustable hood, accessible vents and compatible pockets may be useful for exposure and equipment. Pit zips can help manage heat and moisture, but not every shell includes them.
What it deliberately gives up
A waterproof barrier can feel less comfortable than a more air-permeable layer in some dry-weather conditions. Fabric feel, stretch, noise and ventilation vary by garment; not every hardshell is stiff or uncomfortable.
Buying one for dry-weather use is the classic category mistake. If your realistic use is showers on a dog walk, a lighter rain jacket or even a water-resistant windproof will be worn more and complained about less. The hardshell earns its place when the forecast is genuinely bad and you are going anyway.