TPX meaning is Textile Paper. This was the paper version of the Cotton TCX colours in the Pantone Fashion, Home +Interiors range until 2015.
TPX is the old suffix for the textile colours on paper, it has now been replaced by TPG, the 2100 colours in the TPX range prior to the change to TPG have been retained in the TPG book and are approximately the same colour even though reformulated.
The suffix changed from TPX to TPG in 2016 because Pantone had to prove to the EU governments that they had removed banned chemicals from the coating process. All lead pigments and chromium have been removed to ensure compliance with environmental requirements.
If you have a TPX book this is obsolete and should be replaced with a TPG book, 700 colours have been added since the change from TPX and so you are missing out on colours for your creativity!
TPG colours are found in the Paper Traveler, Color Guide, Color Specifier and as individual TPG sheets.