This one seems to scare a lot of people out there. I get it. It seems like the dumbest question possible, but it's not. Not long ago, I didn't know the difference either. I also once upon a time couldn't differentiate between apple slices and rocks or dogs and grass - just into the mouth it went. It took a kind person to teach me to not eat sand and tell me why I have to keep my pants on at the grocery store. So now that we're adults we are just expected to know stuff? No. The Googles have helped with some of that awkwardness but they can be conflicting and offer too many rabbit holes leading to pointless adventures, so let me help.
The tricky part about soil and dirt is that they're not quite as polarized as apple slices and rocks. They share quite a few similar characteristics and thus, the line where dirt ends and soil begins is a little mangled. Mostly, what differentiates them is just horse-piss terminology but I'll share what I know and then you can make an informed decision about whether or not you are going to adopt soil into your personal word inventory.
Dirt is crumbly earth stuff. Dirt can be an array of shades ranging from red to brown to tan to ashy grey. Basically dirt looks like varying degrees of earthy tones (hmmm) and is almost everywhere when you're in the world and on solid ground. Dirt is usually mixed with stones and little rocks and is pathetically nutrient deficient. Dirt is often sad and alone, with very few, if any, little green dudes growing in it. If dirt wasn't such an uninhabitable dead zone, then maybe it wouldn't be the playground for tumbleweeds and dehydrated dying people.
Soil, contrary to dirt, is special earth matter that you use to grow stuff on purpose. It is a precious tool employed for gardening of all kinds. Soil is dark-ass brown, has very few, if any rocks, and has decomposed organic matter squirming through it. Most people don't buy dirt but many buy soil because other people make it and that means it costs money. In theory, you could buy soil, plunk some plants into it and grow some food. However, although there is some composted organic stuff, store bought soil often needs a boost of added compost (fertilizer) to really get you growing successfully. Okokok, so compost looks like soil too so what's the difference then......?
Compost ('post) is nutrient dense decomposed plant and food matter. Compost sits at that nice level where all that lovely plant stuff has recently broken down to a point where its original ingredients (rank lettuce, egg shells, sweaty cheese) is undetectable. Now you have sweet smelling, crumbly, black gold to add to your soil.
Plants require fertility in their growing medium in order to make food for you. Fruiting plants especially need a shit tonne of energy to produce a decent harvest. Making fruits is the entire purpose of their existence so you best believe they will take all the tasty goodness that soil can offer and suck it dry. When you replant you will need more 'post so your new baby planties will get the nutrient super boost they need.
Generally it is good practice to mix 20% compost into your soil. If you are doing any transplanting (Which you will. Like I always start my own tomatoes from seed. Bitch please) then sprinkle a half handful into the bottom of your planting hole so those roots get food right away. Mmmmmmm old, rotted salad and juice pulp.
So now you know the difference between going outside and grabbing a bucket of dirt to throw in a pot with your new baby aloe and buying some fluffy, nutrient rich soil at the garden shoppe.
Really, it's a fuzzy line, but gardeny types call the stuff they use for planting, soil and all other unimportant, random dust is called dirt.
Also, in case nobody ever told you, don't take your pants off at the grocery store. It's not going to end well for anyone. Unless prison is your thing.
Happy panting and planting,