Used space is essentially the same as allocated space. It is the space used by data files. Because space is allocated in blocks there is some space empty but allocated. For example, a file using 20 bytes may have 512 bytes allocated because it is the minimum allocation. Directory and file information, which track and access your data file also require allocated space. Logical space might mean anything depending on the context. Raw space and Physical space may mean the same thing. This is the actual amount of space on a drive, for example but formatting and space tracking information reduce this amount to a lower Available space amount. Landing space is where the drive reading mechanism comes to rest when a magnetic reading head comes to rest or lands when the drive ceases spinning. Due to probable damage data is not stored in this area. There are lots of other complications. Partitions, bad sectors, ... :-)  

Used space is essentially the same as allocated space. It is the space used by data files. Because space is allocated in blocks there is some space empty but allocated. For example, a file using 20 bytes may have 512 bytes allocated because it is the minimum allocation. Directory and file information, which track and access your data file also require allocated space. Logical space might mean anything depending on the context. Raw space and Physical space may mean the same thing. This is the actual amount of space on a drive, for example but formatting and space tracking information reduce this amount to a lower Available space amount. Landing space is where the drive reading mechanism comes to rest when a magnetic reading head comes to rest or lands when the drive ceases spinning. Due to probable damage data is not stored in this area. There are lots of other complications. Partitions, bad sectors, ... :-)