WHAT DOES BERSA MINI THUNDER 9 MEAN?

I preferred both equally of my Bersa handguns a great deal of I purchased My Daughter a Thunder .22 Lr . And he or she enjoys hers . And at last I just acquired a Thunder.40 UC pro …And so far I have not experienced a difficulty using this type of one both by about five hundred rounds down Array … I feel That the Bersa line of handguns are a nu