I will take a shot at explaining, although I am sure some of the Veeam team members will correct me!
Data Read = That is the total drive size, listed as 50GB you most likely have a 50GB volume size
Transferred = That is the amount of data the backup job transferred to the destination. This will be much smaller than the Data Read because it does not need to copy all the data each time it backups, just the small incremental changes.
Backup Size = For me this is usually close to the Transferred size, but Backup Size lists the actual size on disk that the backup job used which disk usage sizes can vary from the true data size that was transferred.
Dedupe = Deduplication is the process of using similar data blocks and only making a single copy of them so you can have smaller backups for each jobs. In VEB this doesn't apply much because each VEB job is a single server. When you use VBR and you set a backup job to backup multiple virtual servers that were created with the same image this saves a bunch of backup space. Think of 5 servers that all have the same C:\Windows folder. In deduplication it would only backup 1 copy of that folder even though 5 servers use it. In a VEB job I would not expect this value to vary much as it only backs up a single server per job.
Compression = This process decresease the size of the backup on disk, so it takes all the backup data and compresses it to a smaller size to save space.
Hope that helps,