The SD Assisciation (SDA), which handles the specification for SD cards of all types, has unveiled its latest spec, SD 5.1, including a new distinction for SD cards that are designed for application use rather than just media storage. The new specification, called "A1" (or App Performance Class 1), shows that a given SD card meets certain performance standards set by the SDA that determine it's good enough to be used as a storage device for apps.
The new SD 5.1 spec comes as a (much delayed) response to Android 6.0 Marshmallow's introduction of Adoptable Storage in which an Android device can fully adopt an SD card as part of the internal storage rather than simple removable media. As many people have found, using a cheap or slow SD card in a device that's using Adoptable Storage can be detrimental to the experience of the whole phone.
In order for an SD card to be considered A1 compliant, it has to provide random read IOPS (input-output access per second) of 1500, write IOPS of 500 and sustained sequential performance of 10MB/s. Though many high-end cards will already meet these standards, some on the bubble that purport to have greater speeds may not actually offer them in a sustained manor or be able to offer high enough IOPS performance for regular app use.
Adding another level to this is a certification process for phones and tablets themselves to be considered A1 compliant. The SDA will offer manufacturers the opportunity to test their phone or tablet's own hardware to make sure it can accept these speeds for an optimal Adoptable Storage experience, though the cards themselves are far more often the weak point in this equation.
The A1 badge, which you can see above, will soon be found on packaging for SD cards and potentially phones and tablets that have passed the certification process from the SDA. As higher speed needs emerge, the SDA has said it plans to introduce higher levels of compatibility, i.e. A2, A3 and so on.