Sequential read/write speeds are measured in MB/s (Mega Bytes per Second), whereas random read/write speeds are measured in IOPS (Input/output Operations per Second).
Both units represent the amount of data input and output that can be processed in a second, and therefore larger numbers indicate higher speeds.
A sequential write speed is measured in MB/s, and a random write speed is measured in IOPS, and in both cases, larger numbers indicate better performance.