What is "fasting day"

Fast \Fast\, v. i. [imp. & p. p. Fasted; p. pr. & vb. n. Fasting.] [AS. f[ae]stan; akin to D. vasten, OHG. fast[=e]n, G. fasten, Icel. & Sw. fasta, Dan. faste, Goth. fastan to keep, observe, fast, and prob. to E. fast firm.]

1. To abstain from food; to omit to take nourishment in whole or in part; to go hungry.

   Fasting he went to sleep, and fasting waked.
   --Milton.

2. To practice abstinence as a religious exercise or duty; to abstain from food voluntarily for a time, for the mortification of the body or appetites, or as a token of grief, or humiliation and penitence.

   Thou didst fast and weep for the child.
   --2 Sam. xii. 21.

   Fasting day, a fast day; a day of fasting.