Storage that divides data into fixed-size blocks, like a traditional hard drive. Like having a parking garage with numbered spaces - each space is the same size and has a specific address.
AWS EBS provides block storage for databases and applications that need the performance of a local hard drive but in the cloud.
All four provide attachable, low-latency block devices for VMs (and some managed services). They support performance tiers, snapshots/backups, encryption, and can be resized. Differences are mainly in performance options (IOPS/throughput tiers), attachment limits, and regional/zonal availability.