Modify the content of the backup method

Author: jimcat8

docs/books/admin_guide/09-backups.md

@@ -69,10 +69,13 @@ In addition to the above mentioned issues, system administrator should also cons
 
 ### Backup methods
 
-* **Complete**: one or more **filesystems** are backed up (kernel, data, utilities, ...).
-* **Partial**: one or more **files** are backed up (configurations, directories, ...).
-* **Differential**: only files modified since the last **complete** backup are backed up.
-* **Incremental**: only files modified since the last backup are backed up.
+* **Full backup**: refers to a one-time copy of all files, folders or data in the hard disk or database.
+* **Incremental backup**: refers to the backup of the data updated after the last Full backup or Incremental backup.  
+* **Differential backup**: Refers to the backup of the changed files after the Full backup.
+* **Selective backup (Partial backup)**: Refers to backing up a part of the system.
+* **Cold backup**: refers to the backup when the system is in shutdown or maintenance state.  The backed up data is exactly the same as the data in the system during this period.
+* **Hot backup**: Refers to the backup when the system is in normal operation.  As the data in the system is updated at any time, the backed-up data has a certain lag relative to the real data of the system.
+* **Remote backup**: refers to backing up data in another geographic location to avoid data loss and service interruption caused by fire, natural disasters, theft, etc.
 
 ### Periodicity