Rolling onto their back can be a sign of submission or deference. By exposing their vulnerable belly, a dog is showing that they trust and respect the other individual (human or dog) and are not a threat.
During playtime, dogs might roll onto their backs to signal that they want to engage in play or to invite their playmate to continue the interaction.
Dogs are social animals, and rolling on their back can be a form of social communication. It can be a way to initiate interaction or to invite a playmate to join in.
Rolling on their back can be a way for dogs to seek attention from their owners. This behavior can be accompanied by wagging tails, nuzzling, or even vocalizations.
If a dog has an itch or discomfort on their back or belly, they might roll to try and alleviate the irritation. This could be due to allergies, bug bites, or other skin conditions.
Dogs have scent glands in their backs and may roll on objects or surfaces to transfer their scent. This can be a way to mark their territory.
Dogs have fewer sweat glands than humans, so rolling on a cool surface can help them regulate their body temperature, especially on a hot day.
Rolling on their back can be a way for dogs to stretch out their muscles, particularly their back and abdominal muscles.