What is a Scene?

Everyone knows what they are, right? No, I don't mean the 2y.o throwing a tantrum at the checkout because you chose the one with the sweets stacked up and by mistake and won't buy them one, or them pulling the bottom can from the artful stack at the end of the aisle in the supermarket and sending them flying... or maybe I do, after all they are scenes.

A scene I am told happens in immediate time... i.e. it shows rather than tells, unfolding an event to the reader as it occurs rather than described after the fact...
They have settings, specific locations that the reader can picture.
They also have action, something happens.... as it moves the story forward.
They must also have a consistent point of view.

So, you may say, my examples above contain all of those... there is only one thing... they are narrative summary of a scene. With its omnipotent POV it can bring a picture to the readers mind but it is only specific to that readers memory of when they saw, or how they imagine that action, i.e. no specific supermarket, no specific character other than a 2 yo, no dialogue.... A scene must engage the reader actively, and is much harder for a writer to achieve, and usually takes more space.
Let's take the supermarket scene again....

It was the end of a long day, the last thing Sally-Ann needed as she placed a protesting Cassie in the front of the trolley was a trip to the The Village Supermarket, and decide what to give the picky two year-old for dinner. She was sick of noodles, steamed broccoli and carrots.
"Help Mommy here honey, what do you want for dinner," she said tiredly, in the vague hope that Cassie, who had woken up cranky from her nap at daycare, would answer.
"Noodles," came around the thumb and grubby blankie shoved in her mouth.
"How about fish...?"
"Noodles," came out at a slightly higher pitch.
She knew it crazy to try to reason with a two-year old but out it came. "We had noodles last night."
"Noodles, Noodles...." the bottom lip quivered then stilled as her eyes alighted on the bright red labels within arms reach.
Huh-Oh, the hand went out and before she could reach over the trolley to stop her, Cassie's two year old fingers had become, octopus tentacles about the can of tomatoes near the bottom of the stack arranged at the end of the aisle.
"Honey, you don't like tomatoes," she attempts persuasively trying to pry the fingers loose before the stack tumbles down around their ears.
Too late. In slow motion an implosive domino effect takes place. Horrified, she throws herself over Cassie to protect her. Nothing will stop this mini metallic avalanche rolling to the four corners of the checkout area.
Cassie's delighted chuckle follows the last can rolling down the nearest aisle to hit the freezer.
Sally-Ann looked with red-faced apology at those staring at them as shop assistants raced toward them.
"Tomatoes...." Cassie demanded.
She bent down, scooped up a dented can and headed for the nearest checkout miraculously vacated for her. Tomorrow, she vowed, she'd shop before she picked Cassie up and at another supermarket.

So here you have a specific scene, from Sally-Ann's POV, action, dialogue, a beginning a middle and end...