Instance Family
The category of EC2 instance types, such as compute-optimised, memory-optimised, or storage-optimised, each priced and performance-tuned for a different workload profile.
Definition
An Instance Family groups EC2 instance types by the hardware profile they're tuned for: general purpose (M-series), compute-optimised (C-series), memory-optimised (R-series), and storage-optimised (I-series), among others. Choosing the wrong family for a workload is a common source of both poor performance and wasted spend; a memory-hungry application running on a compute-optimised instance will often need to scale up further than necessary just to compensate.
In Practice
A Redis caching layer with heavy memory demands but light CPU usage is typically better served by an R-series instance than the default M-series most teams reach for first.