“standard filters” are cool. Well, not very, because there are still a lot of things they cannot do, and they aren’t as standard as the name implies. But, they can be handy.
All you really have to do is google the term to find out more, but basically you can get a wide variety of filter cartridges for standard filter housings, so you can put together your own filter system fairly cheaply, and allowing you to take advantage of a variety of filter technologies from various manufacturers. The filter housing is the pressure containment vessel that surrounds the actual filter media. You can get transparent ones. You can get “Jumbo” sized ones, which are a larger diameter. For granular filter media like ion exchange resin or granular activated carbon, you can buy a cartridge that you put the raw filter media into, and it has filter screens to prevent the carbon or whatever from getting out.
The filters and housings are available in a variety of lengths, 10″ 20″, even 40″.
There are other types of filter housings, too. There are pool filter housings, if you needed a really big filter.
You can also get stainless steel ones, and ones for cross flow (e.g. reverse osmosis) filtration, but those are are not referred to as “standard” housings.