Something will already have happened before a certain time in the future
Form
will + have + past participle
Example
I will have written the letter by tomorrow.
Practice here
Holy
(adj): Sacred, divine, blessed.
Holiday: a holy or festive day; a day off, vacation (also sacred)
Expressions: Holy Cow! Literally true in India.
Ex: Holly Mackerel! Delicious, healthy and full of mercury.