Fingerspelling was a manual alphabet wherein each letter or number was represented by a sign. These signs were formed using the hand and fingers. The right combination of letter signs could produce a word unit. Fingerspelling was accompanied with speech on lip movement and sign language.
A portion of a guide on fingerspelling was seen in the Context Indices when Data was reviewing the file on the non-verbal language (gestural) M-9 in 2365. (TNG: "Loud As A Whisper")