This is the 860th most frequent Russian word.
каждый
"Каждый" means "each" or "every" in English.
Here, 'каждый' is an adjective modifying 'день', meaning 'every', and indicates frequency.
Каждый день я посещаю парк.
Every day I visit the park.
In this sentence, 'каждый' modifies 'учитель', meaning 'each', and emphasizes individual participation in the discussion.
На собрании высказался каждый учитель.
At the meeting, each teacher spoke.
Here, 'каждый' is used as a pronoun meaning 'each', and denotes every individual in a group.