explain table variable in briefly with examples

SELECT  distinct Profile,stuff((select distinct ', '  +  Specialization  FROM TM_Specialization tms INNER JOIN TM_Profile tmp
ON tms.ProfileID=tmp.ProfileID where tms.ProfileID =tm_p.ProfileID
FOR XML PATH('')
) ,1,1,'') as Specialization
FROM TM_Profile TM_P INNER JOIN  TM_Specialization TM_s
ON TM_S.ProfileID=TM_P.ProfileID