Gramogram

Hello

I’m wondering about ‘Gramograms’, these are ‘letter words’ such as ‘ICQ’ (I seek you), ‘m8’ (mate), ‘b4’ (before), ‘OL’ (oh well)… I guess even ‘u’ (you).

Do these fall under ‘abbreviations’? Or ‘unusual words’? Or ‘pronunciation’?

Thanks

Sarah