macron

pituusmerkki puhekieltä A short, straight, horizontal diacritical mark (¯) placed over any of various letters. It usually is used to indicate that the pronunciation of the vowel is long; in Mandarin pinyin (Chinese), it indicates the first tone, e.g. chūzūchē.
1986: Peter V. Jones and Keith C. Sidwell, Reading Latin: Grammar, vocabulary and exercises, Introduction — General notes (note 1), page 2 (22nd printing (2007); Cambridge University Press; ISBN 9780521286220)

All vowels are pronounced short unless marked with a ¯ (macron) over them. So observe different vowel length of ‘i ’ in, e.g., fīlia, etc. It may be helpful, but is not essential, to mark macra in your exercises.