Okay, these terminologies might sound very similar, but they aren’t. It’s actually both simple, and complex. Let us explain.
AOSP stands for Android Open Source Project. It is the most barebone, most basic version of Android as built by the Android development team at Google. AOSP is often referred to as ‘Vanilla Android’. AOSP consists only the codes needed for the OS to boot up & just function. No bloatware, no GApps, no third party patches and libraries, no extra features and tweaks. AOSP serves as the base for ROM development by OEMs. In the past, AOSP came preloaded in phones like the first Galaxy Nexus, but with advancements in the Android ecosphere, AOSP can only be flashed manually as all manufacturers decide to ship their phones with their customized skins. Also, because AOSP is very barebone and lacks CPU libs and patches, it won’t even be able to boot on most phones in its stock form.
Stock Android is very easily confused with AOSP these days, but there’s a significant difference. Back in 2012-13 when Android was just gaining pace and market share, AOSP was called stock Android as well, but with the introduction of Google’s own smartphone brands, then Nexus and now Pixel, the term ‘Stock Android’ is now defined as the flavor of Android Google uses on its Pixel smartphones. It is basically AOSP with Google services, apps, features & modifications included. So, the variant of AOSP used on Google’s Pixel lineup is referred to as Stock Android.
Android phone manufacturers gain AOSP and Google apps & services from Google, add additional features and modifications, and then bundle this modified customized OS with their phones. These ROMs that come pre-installed on the phones from the factory are called the respective devices’ Stock ROMs. Stock ROMs vary from manufacturer to manufacturer, and in some cases, device to device as well. Take, for example, most Xiaomi phones (except the Android One and the Android Go phones) ship with MIUI installed, which is why MIUI is called the stock ROM for Xiaomi devices. But let’s take another example. Let’s consider the Samsung Galaxy S7 and the Galaxy S10. Although both devices are made by the same manufacturer: Samsung, the S7 launched with TouchWiz UI while the S10 launched with the newer One UI. So, the stock ROM for the S7 would be TouchWiz, whereas, for the S10, it would be One UI. Actually, if you think about it, Stock Android is the stock ROM for Pixel smartphones. Put simply, the variant or flavor of Android that is present on the phone when you take it out of the box for the first time is it’s stock ROM. Most manufacturers also keep adding updates to the stock ROMs via OTAs, which means your stock ROM doesn’t always have to be the same old OS with outdated features & security patches, but can also be the same base OS with updated features and patches. Manufacturers name their stock ROMs differently, like Xiaomi calls their ROM MIUI, while Samsung named it One UI. Honor calls their ROM EMUI whereas Oppo decided to call it ColorOS. But, we guess you know now what stock ROM means.
Be sure to check the following knowledge-base articles as well. A little extra knowledge never hurts!
> Stock ROMs vs Custom ROMs
> Are Custom ROMs Secure?
> Can custom ROMs be installed without rooting?
Hope it helped. Go flash!