Class 10 is a rating designed for writing speed, for the time it takes for data to be "downloaded" to your microSD card for storage. The speed class of 10 refers to the file transfer speed of 10 MB/s, the ideal "workload" for uploading 720p, 1080p, and 4K video at an acceptable pace without losing patience. The next class up is Class 30, or 30 MB/s. For more intensive applications using 8K video at 60/120fps, higher classes transferring 60MB/s and 90MB/s are highly recommended. Avoid "Class 2" cards and go for a minimum of Class 10 to notice the difference.