The word solfegietto means a little exercise or study. The most famous use of this word is in a keyboard piece by C.P.E. Bach. It is from the 18th century Italian word solfeggiare which, according to Collins Dictionary (Online) means as follows. (Links left in for access to the source)
Word forms: plural-feggi (-ˈfɛdʒiː), -feggios or -fègesmusic
Therefore this first set of three small exercises for flute use this name.