Someone changed that in your database — this is the default label definition — “Identifier”.
The default settings are defined in this code snippet below. The first entry is the gettext() entry for the label for that field.
You’ll need to change it in the SQL extendo meta table.
__( 'Identifier' ,'slp-power' ),
'addon' => $this->addon->short_slug ,
'slug' => 'identifier' ,
'display_type' => 'text' ,
'help_text' => __( 'The identifier field is meant to store a unique location record ID from an external data source. ' , 'slp-power' ) .
__( 'During a CSV import, this field is used to match up incoming data with existing locations. ' , 'slp-power' )