The first letter of the acronym describes the overall screening. The second letter describes the screening of individual pairs and the TP refers to the Twisted Pairs.
The reason for the additional letter at the beginning of the acronym is to avoid confusion of the different types of screened cables which have been developed in the last few years.
Example - F/UTP
F - Describes the overall screen
U - Describes the screening of the pairs
TP - Describes the Twisted pairs
Different types of screening
U - Unscreened
F - Foil screening
S - Screened Braid
Unscreened outer with unscreened twisted pairs
Screened foil outer with unscreened twisted pairs.
Unscreened outer with individual screened foil twisted pairs
Screened braid and foil outer with unscreened twisted pairs
Screened braid outer with individual screened foil pairs.
Screened foil outer with individual screened foil twisted pairs