'Mat Salleh' WORD

Assalamualaikum , holla all .. Today i watch a few videos in youtube .. There a malay word which is 'Mat Salleh' whose refer to english people .. I don't know where the Malaysian learn that word .. I think i heard or read somewhere before that 'Mat Salleh' word refer to English word(I don't know what word is that) but when that person pronounce that word too fast , the word become 'Mat Salleh' .. So cuz of that the word 'Mat Salleh'known all to Malaysian .. I'm sorry if I'm wrong or what .. That from my view .. So, that's it ! Bye .. Love,Aby ..