DOWS meaning in T-SQL
It is the table_alias as shown in the documentation for the FROM clause.



[ FROM {  } [ ,...n ] ]   
 ::=   
{  
    table_or_view_name [ [ AS ] table_alias ]   
        [  ]   
        [ WITH (  [ [ , ]...n ] ) ]   
    | rowset_function [ [ AS ] table_alias ]   
        [ ( bulk_column_alias [ ,...n ] ) ]   
    | user_defined_function [ [ AS ] table_alias ]  
    | OPENXML    
    | derived_table [ [ AS ] table_alias ] [ ( column_alias [ ,...n ] ) ]   
    |    
    |    
    |   
    | @variable [ [ AS ] table_alias ]  
    | @variable.function_call ( expression [ ,...n ] )   
        [ [ AS ] table_alias ] [ (column_alias [ ,...n ] ) ]  
    | FOR SYSTEM_TIME    
}  



It would be clearer if the code author had chosen to use the optional AS keyword, and to use the alias elsewhere in the query:

SELECT 
    DOWS.wait_type,
    SUM(DOWS.wait_time_ms / 1000) AS [wait_time_s]
FROM sys.dm_os_wait_stats AS DOWS
WHERE 
    DOWS.wait_type NOT IN 
    ( 
        'SLEEP_TASK', 'BROKER_TASK_STOP',
        'SQLTRACE_BUFFER_FLUSH', 'CLR_AUTO_EVENT',
        'CLR_MANUAL_EVENT', 'LAZYWRITER_SLEEP' 
    )
GROUP BY 
    DOWS.wait_type
ORDER BY 
    SUM(DOWS.wait_time_ms) DESC;