# Glossary
### .CSM
Each table with the **CSV Storage Engine** has `.CSM` file which contains the metadata of it.
### .CSV
Each table with the **CSV Storage** engine has `.CSV` file which contains the data of it (which is a standard Comma Separated Value file).
### .exp
Files with the `.exp` extension are created by **Percona XtraBackup** per each _InnoDB_ tablespace when the [`--export`](xtrabackup-option-reference.md#–-export) option is used on prepare. See [restore individual tables](restore-individual-tables.md).
### .frm
For each table, the server will create a file with the `.frm` extension containing the table definition (for all storage engines).
## General availability (GA)
A finalized version of the product which is made available to the general public. It is the final stage in the software release cycle.
### .ibd
On a multiple tablespace setup ([innodb\_file\_per\_table] enabled), _MySQL_ will store each newly created table on a file with a `.ibd` extension.
### .MRG
Each table using the **MERGE** storage engine, besides of a `.frm` file,
will have `.MRG` file containing the names of the _MyISAM_ tables
associated with it.
### .MYD
Each _MyISAM_ table has `.MYD` (MYData) file which contains the data on it.
### .MYI
Each _MyISAM_ table has `.MYI` (MYIndex) file which contains the table’s indexes.
### .opt
_MySQL_ stores options of a database (like charset) in a file with a `.opt` extension in the database directory.
### .par
Each partitioned table has `.par` file which contains metadata about the partitions.
### .TRG
The file contains the triggers associated with a table, for example, `\mytable.TRG`. With the `.TRN` file, they represent all the trigger definitions.
### .TRN
The file contains the names of triggers that are associated with a table, for example, `\mytable.TRN`. With the `.TRG` file, they represent all the trigger definitions.
### backup
The process of copying data or tables to be stored in a different location.
### compression
The method that produces backups in a reduced size.
### configuration file
The file that contains the server startup options.
### crash
An unexpected shutdown which does not allow the normal server shutdown cleanup activities.
### crash recovery
The actions that occur when MySQL is restarted after a crash.
### data dictionary
The metadata for the tables, indexes, and table columns stored in the InnoDB system tablespace.
### datadir
The directory in which the database server stores its data files. Most Linux distribution use `/var/lib/mysql` by default.
### full backup
A backup that contains the complete source data from an instance.
### ibdata
The default prefix for tablespace files. For example, `ibdata1` is a 10MB auto-extensible file that _MySQL_ creates for a shared tablespace by default.
### incremental backup
A backup stores data from a specific point in time.
### InnoDB
Storage engine which provides ACID-compliant transactions and foreign
key support, among others improvements over _MyISAM_. It is the default
engine for _MySQL_ as of the 8.0 series.
### innodb\_buffer\_pool\_size
The size in bytes of the memory buffer to cache data and indexes of _InnoDB_’s tables. This aims to reduce disk access to provide better performance.
> \[mysqld\]
> innodb\_buffer\_pool\_size=8MB
### innodb\_data\_home\_dir
The directory (relative to `datadir`) where the database server stores
the files in a shared tablespace setup. This option does not affect the location of `innodb\_file\_per\_table`. For example:
> \[mysqld\]
> innodb\_data\_home\_dir = ./
### innodb\_data\_file\_path
Specifies the names, sizes and location of shared tablespace files:
> \[mysqld\]
> innodb\_data\_file\_path=ibdata1:50M;ibdata2:50M:autoextend
### innodb\_file\_per\_table
By default, InnoDB creates tables and indexes in a [file-per-tablespace](https://dev.mysql.com/doc/refman/8.0/en/innodb-file-per-table-tablespaces.html). If the `innodb_file_per_table` variable is disabled, you can enable the variable in your configuration file:
> \[mysqld\]
> innodb\_file\_per\_table
> or
> start the server with `--innodb_file_per_table`.
### innodb\_log\_group\_home\_dir
Specifies the location of the _InnoDB_ log files:
> \[mysqld\]
> innodb\_log\_group\_home=/var/lib/mysql
### logical backup
A backup which contains a set of SQL statements. The statements can be used to recreate the databases.
### LSN
Each InnoDB page contains a log sequence number(LSN). The LSN is the system version number for the database. Each page’s LSN shows how recently it was changed.
### my.cnf
The database server’s main configuration file. Most Linux distributions place it as `/etc/mysql/my.cnf` or `/etc/my.cnf`, but the location and name depends on the particular installation. Note that this method is not the only way of configuring the server, some systems rely on the command options.
### MyISAM
The _MySQL_ default storage engine until version 5.5. It doesn’t fully
support transactions but in some scenarios may be faster than _InnoDB_.
Each table is stored on disk in 3 files: `.frm`, `.MYD`, `.MYI`.
### physical backup
A backup that copies the data files.
### point in time recovery
This method restores the data into the state it was at any selected point of time.
### prepared backup
A consistent set of backup data that is ready to be restored.
### restore
Copies the database backups taken using the backup command to the original location or a different location. A restore returns data that has been either lost, corrupted, or stolen to the original condition at a specific point in time.
### Tech preview
A tech preview item can be a feature, a variable, or a value within a variable. Before using this feature in production, we recommend that you test restoring production from physical backups in your environment and also use an alternative backup method for redundancy. A tech preview item is included in a release for users to provide feedback. The item is either updated and released as [general availability(GA)](#general-availability-ga) or removed if not useful. The functionality can change from tech preview to GA.
### xbcrypt
To support the encryption and the decryption of the backups, a new tool xbcrypt was introduced to **Percona XtraBackup**. This utility has been modeled after the **xbstream** binary to perform encryption and decryption outside **Percona XtraBackup**.
### xbstream
To support simultaneous compression and streaming, **Percona XtraBackup** uses the **xbstream** format. For more information see [xbstream](xbstream-binary-overview.md)
### XtraDB
_Percona XtraDB_ is an enhanced version of the InnoDB storage engine, designed to better scale on modern hardware. _Percona XtraDB_ includes features which are useful in a high performance environment. It is fully backward-compatible, and is a drop-in replacement for the standard InnoDB storage engine. For more information, see [The Percona XtraDB Storage Engine](https://www.percona.com/doc/percona-server/8.0/percona_xtradb.html).
### Zstandard (ZSTD)
`ZSTD` is a fast lossless compression algorithm that targets real-time compression scenarios and better compression ratios.
`ZSTD` compression algorithm was implemented in [Percona XtraBackup 8.0.30-23](release-notes/8.0/8.0.30-23.0.md).