It's a word that has multiple consonant sounds together. Look at the consonants at the starts of these words: fly /fl/ train /tr/ squirrel /skw/ throw /thr/.

On-air challenge: Every answer today is a six-letter word or name that has four vowels and two consonants and is pronounced in four syllables. Ex. Absolute madness --> IDIOCY. 1. Perfect world. 2 ...