As best I can describe them... which will probably be as clear as mud.

Easiest way is probably to start with the assumption that sourdough is basically bread that is made without the addition of those little packets of yeast you see at the store. Instead it gets it's leavening action from sourdough starter (although I do supplement some of my recipes with additional yeast from packets).

Sourdough starter is created by mixing water & flour and letting them sit lightly covered in your kitchen where naturally occuring yeasts in the environment can find it & set up shop - which you'll see when the goo starts to bubble and grow. (And hopefully good yeasts find it instead of the ones that get yucky!) The wild yeasts set up residence in the jar & start reproducing like rabbits on viagra!

The problem is all that reproduction (seen by increasing bubbles & activity) uses up a LOT of energy so the starter must be fed. Left unfed, it will consume every bit of sugar it can find and eventually starve itself to death.

So how do you feed the starter? It's a hungry beast & needs a lot of food! Essentially, you feed it an amount of flour & water (differennt sites tell you different proportions of each but the total must equal the amount of starter you want to have).

Just toss it in the jar & stir. After mixing, you now have twice as much starter as you did before feeding. Which is cool to a point BUT... if something isn't done, Sir Starter will quickly outgrow his jar/abode and be running over the edges! Not to mention the amount that would be needed to keep him fat & happy!

Example:
Day 1 (1/2 cup starter) - feed 1/2 cup flour/water
Day 2 (1 cup starter) - feed 1 cup flour/water
Day 3 (2 cups starter) - feed 2 cups flour/water
Day 4 (4 cups starter) - feed 4 cups flour/water
Day 5 (8 cups starter) - feed 8 cups flour/water

You get the idea. So unless you're making bread/waffles/pizza dough/whatever every single day, you've gotta keep your amount of starter at a reasonable level.

You're only choices for doing so are to discard or slow the reproduction process by refrigerating (which is only practical if you know for certain you won't want to bake any in the next 24 hours because it takes that long to warm up & reactivate). Most people choose to discard by pouring off half their starter and "discarding" it.

Discard can mean "toss it in the trash," "put it in the jar in the frig for later use," or "go on & make something from it now." You can pass it along to a friend as their new starter, dehydrate it (for a powdered starter), or I've even heard of folks freezing it. There are also tons of sourdough discard recipes out there - I just still don't understand the difference between them and regular sourdough recipes...

Anyway, that's what a discard is. Are you confused yet???

p.s. Wish me luck. I've got a huge sandwich bread size loaf on it's second rise right now. New recipe. New technique. And my first time using a Pullman baking pan. First rise was impressive - it easily tripled in size!!!