There are different types and styles of hydroponics, and the terminology is difficult to stretch to fit every type. I deal only with relatively small indoor hydroponics, and the four systems I'm familiar with use essentially the same equipment, though not the same sizes or shapes. Our discussion must start with the Container. If you don't have a Container of some sort to hold the water, you don't have hydroponics. You're outside (or indoors) gardening in dirt. Every manufacturer makes multiple sizes and shapes of Containers. I will start with the system I no longer have, the 2022 QYO 12-pod system.
As shown in the diagram, the QYO 2022 Container is rectangular, 7.2" wide by 15.4" long and 3.3" deep. It holds roughly 4 liters of water. The Container supports a Deck which contains Pod Bays and possibly other accessories such as a Fill Port. These features are common to most systems. The QYO has a float operated Level Indicator that rises from the deck. The QYO 2022 has 12 square Pod Bays arranged in an offset pattern around the central Light Mast. All my systems have a Light Mast, but QYO is the only one with it in the center of the Deck. Many other systems have no masts because the lights are suspended above the plants in some way. That sort of arrangement permits growing tall plants.
The diagram is labeled with iDOO's proprietary names. They call the Deck the Water Tank Cover. I frankly can't tell if they are calling the Pod Bays "Basket Containers." I assume so. There are 12 in a rectangular rank and file arrangement. Their name for the Fill Port is "Water Fill Opening" and it has a hinged cover that pivots out of the way. iDOO's Level Indicator is a viewport in the front of the unit. iDOO's Light Mast attaches at the back, permitting the Deck to be removed without removing it.
This other system is the iDOO Upgraded 2 in 1 Hydroponics Growing System, 6 Pods Hydro Indoor Herb Garden with LED Grow Lights, Adjustable Height, Automatic Timer, Plants Germination Kit for Kitchen, Countertop, White. (What a name!) It could be used for soil with a built-in watering tank, or like the picture, strictly hydroponic. As a hydroponic unit, it has a bucket within the bucket for the water Container. It's round, rather than rectangular. I called mine "the Bucket" and named it Sheba (for she-bucket). The Deck has six Pod Bays and a Fill Port identical to the other iDOOs. The Pod Bays are arranged with one in the center and five in a ring around it. It lacks level indication of any sort. You can look in the Fill Port. The Light Mast is flexible for adjusting the height.
Our next system is the AeroGarden Harvest, one of a dozen indoor units AeroGarden (AG) sells. Looking at the drawing, AG calls the Container the Bowl, which is as good a name for the container of water as any. I'll stick with Container for consistency. They call the normal Deck the "Grow Deck." To be fair, this is because they have interchangeable Decks for starting seeds. The one shown is the regular one, with six Pod Bays and a trapezoidal Fill Port. The Fill Port is also the Level Indicator. You lift it and look inside. There is a post with a flat sign that reads "Fill To Here." The level is also monitored by sensors in the base that should give a visual blinking red alarm when the water is low. I saw that once while attempting to set up the reservoir siphon. The Light Mast is attached to the base, and may be extended to 11" tall.
The Click & Grow™ (C&G) Smart Garden-3 (SG3) is roughly the size of a shoe box. It uses the Kratky method. All the other units discussed have pumps for circulation and aeration - the SG3s do not. All the iDOO units have fans to assist in pollination - the SG3s do not. The SG3 Deck has no dedicated Fill Port. You pour water onto the Level Indicator float and it fills around the float. The Light Mast attaches at the back. It comes with two extentions for raising the lights. One extension is shown in the diagram.
That covers the basic support system. A Container with a Deck which contains Pod Bays and a Fill Port and some kind of Level Indicator and a Light Mast topped with some kind of grow lights. Controls vary from system to system. All seem to have a timer in the lighting system that allows for an extended "day." Some system controls let you select a shorter "day" for flowers than for vegetables. Now we need something to put in the Pod Bays. Growing things is the point - we haven't gotten there, yet.
The drawings are from iDOO, but all the systems use the same basics. There is a Basket. The Basket contains a Sponge. The sponge contains seeds (which you may have to supply). The basket with sponge and seeds is topped by a basket cover. Before germination, the Seed Pod is covered by a Dome. (The iDOO diagram does not show applying a cover.)
Contrast the iDOO seed pods with the AeroGarden seed pods. The picture is taken from an Amazon advertisement, more informed pictorially than the AeroGarden website. All the parts are there, with the names I've used, except the basket covers are a specific form, "Labels." Labels are readily available from AeroGarden and Amazon and elsewhere, but they are not the only basket covers available. I use them, and they aren't my favorites. Let's look at some alternatives.
Any plastic basket cover that fits on the basket will accomplish the purpose of the basket cover, which is to minimize exposure of the sponge to air and airborn spores or bacteria that form mold and algae. The keyhole design is useful for pods that have a thick stalk, like tomato plants. The flexi designs are meant to fit almost anywhere. The aftermarket plastic basket covers have the advantage of being reusable, which the labels do not. However, the labels can be useful on the C&G systems. The SG3 basket is hard plastic with a wick at the bottom. It has a hard basket cover with a wide keyhole. I use labels to reduce that open surface area. The C&G sponges are over two inches across. Read their literature about the Space Age sponges.
The other kind of cover is the Pod Bay Cover. They prevent air coming freely in contact with the water and nutrients through the open hole of an unused Pod Bay. The big picture shows several each of the iDOO and AG models. The iDOO cactus is very cute. There are other designs at Etsy. Neither the QYO nor the SG3 come with pod bay covers. A work-around is to use tinfoil to cover the top of an empty basket. It looks tacky.