Dinner is the name for the main meal of the day, which can be in the middel of the day, or it can be in the evening. If your dinner is in the evening, the midday meal is lunch, and it's not such a substantial meal.

In England anyway, it used to be that, if you had dinner at midday or so, the evening meal would be high tea, with perhaps a bit of supper later on before going to bed.

But these days shared meals as such are quite likely to be replaced by grazing.